How does one overcome a lack of imagination/creativity?

Tequila.

I can be very creative...I cannot do so on demand, however.  Perhaps it is the same with you?

I don't think ADD is necessarily an impediment to creativity.

It depends on what you're creating.

A fine porcelain pot will take intense and sustained concentration for as long as it's on the wheel. But the Zen brushwork to draw bamboo can take seconds.

The moment of inspiration comes in a flash,

first the idea

and then,

striking like lightning,

the sense of

"yes, this is what I want to do."

The key is not to censor it with internal judgements and criticisms like, "no, it's not good enough, it's not original, it doesn't meet the criteria," and so forth. Those judgements act like fortresses to block the flow of ideas. The brain records the moment of blocking and acts to block other ideas before they reach conscious awareness. In the beginning, write down every idea no matter what it is, even if it's funny, ridiculous or impossible. In fact, the more so the better. It doesn't matter how few ideas there are. If there's only one take it and work with it in any way you like. Make a plasticine or clay model of the object. Play with five words with different tones of voice and emphasis, until they become the refrain of a song. Throw unexpected ingredients into the pot and see how its tastes after ten minutes simmering. What starts the flow of creative ideas is the fact of acting and bringing something new into the world. It's like opening a valve. Keep acting on each idea no matter what it is. Some ideas can be destructive. Find a useful place for them, a piece of fiction that speaks about the warps in human nature or a new way to demolish an unsound wall. Give yourself at least half an hour each day to play with bringing unrelated ideas together.

A well-known example of creative or lateral thinking is the Eureka story. Look it up on-line. It shows how two completely unrelated things suddenly come together in the mathematician's mind, leading him to the solution of his problem. There is a specific psychological process underlying the story. First, the thinker is given a seemingly impossible problem. He spends a long time exploring every possible means within his current knowledge and finds the problem too complex. During this time his knowledge and awareness have deepened and he now understands all the variables. He is attuned to the problem so that it is in the back of his mind even when he's unaware of it. Finally, he gives up. In that moment he relaxes, attending instead to some completely unrelated aspect of life. Suddenly something very commonplace happens, something he has seen countless times all his life but without seeing its significance. Now, due to the problem at the back of his mind he sees the significance. Two completely unrelated things have come together unexpectedly to create a solution in his mind. He has invented a new way to solve a previously unsolvable problem.

Only long after the flow of ideas is well established and supported by action, does one begin to judge and evaluate. By then there are too many ideas to bring all to fruition, so one chooses criteria and selects the best. One also learns to analyse the work. Does it work? If so, why and how? If not, why not, and what might improve it? The process of improving may require the same creative processes applied at a more refined level. Usually, the middle stage of creation is the hardest. This is where the problems are, and every solution must fit seamlessly into the whole so that it appears natural and effortless. When an artist finally reaches that stage he or she is becoming competent. Studies of great artists, writers, and composers have shown that it takes five hours or more per day of purposeful practise for ten years in order to reach a world class level of brilliance. But all of us can learn to be more creative in our lives. It is an innate potential in all humans.

Thanks. I've tried searching the net, but I don't find any of it works for me. As in my text, where others can write pages full I can only write a few words. Most of the methods I've found on the internet have an assumed basic level which I have not. They usually involve things like "just write anything" or "just draw something" while saying not to pre-judge it. That doesn't work for me, because nothing comes to mind for me to even have a chance to pre-judge it.

Thank you for this detailed and well considered response.

In simple terms, I find creativity as hard as most people find maths to be, and I find maths to be as simple as most people find creativity, imagination and essay-writing. I have an inverse view of which mental processes are more or less difficult than what appears to be the norm. When I had a tutor for English, they always assumed at first that my issue with with spelling and grammar; I was actually the top of my class in that. No-one has ever been able to help me here because it seems that people can't understand how I could possibly find these things so difficult. By the same token, I've never understood why people complain about maths. To me, the Substitution Rule of Integration in Calculus was simple and logical; only an idiot wouldn't understand (or so my teenage brain at the time thought). I even called the Victorian Education Board, or whatever they were called back then, and asked why we had to do English, when maths was not compulsory (again, I was a teenager then).

When I want to create something, a story, a picture, a character, a song, etc., I struggle to get any ideas at all. The internal prejudgements don't even get to happen (consciously, at least). Basically, as you've put it, my brain blocks most ideas before they reach conscious awareness. It's almost like I have a subconscious filter on any form of creativity.

It's funny, I think the middle stages of things are usually the easiest for me. In programming, once I have a problem and a basic idea, writing the code for it is easy, but it becomes hard again when I need to make that data presentable and well packaged. For a 3d example, animating movements and interactions is easy, but figuring out what to make an animation of and making the models look good are hard.

As a general rule, I tend to work sequentially. In fact, the idea that TV shows and movies are commonly shot out-of-sequence was a shock to me as I couldn't initially understand how you could do that; I still get a little confused by the concept. So, in writing a story back in school, I would generally expect to start writing and write from start to finish. I'd hit a wall because I wouldn't know what the first sentence should be; there were just too many possibilities.

The Eureka moments sometimes happen to me when I'm trying to write a program or similar. When it comes to having something to start with and an end goal, I can usually find my way there. I'm a computer programmer, that's what we do. Give me a start, an end and a few parameters/guidelines, if needed, and I'm fine. On the other hand, too much flexibility can make it impossible. For example, if I was told just to write "a story", I couldn't even start, because the instruction is too vague. I think this is where the ADD comes in; apparently vagueness is the mortal enemy of the ADD mind.

Hopefully, this makes sense as I know my mental processes are unusual.

With me, the only time I am attempting to be creative is on-demand. Generally, if I'm not actively trying to be creative, I'll just be walking around, eating, playing a game, working, etc.; the basic every day things where creative thinking is not required and any mental processes are purely logical.

Since your mind works best along linear paths, maybe try creativity from a linear perspective.

Let's say hypothetically, you'd like to be able to write. A story is chronological, hence moves like a string through time. Try making a list of the events in your life from when you were born. You could mark it in years, or each couple of years. For each year, fill in one sentence which describes the changes that occurred. (If you can't remember, ask your parents or anyone who knew you at the time. Or trawl through old photo albums, family videos, letters, birthday cards or even repair bills. Then, that list becomes your source of starting points. Each sentence is the topic for one story.) Each event has a beginning, middle, and end. In it, something or someone, or some relationship, changes, and you are describing how it happened and how you felt about it. You might also describe what you witnessed of the feelings and reactions of other. Whatever you write, forget about trying to create or invent, and just describe it exactly the way you remember it. Actually, the best stories are written this way. The variations in real life are infinite.

In maths, you would be familiar with fractal algorithms and the plotting of the results of each iteration as coordinates in a graph. When random colours are assigned numerical values, the result is an image of fractal geometry. You might know James Gleik's book which, among other applications, describes how fractal mathematics can describe bifurcation events in physics, the moment when something can flip from one trajectory of movement to another, where predictability drops to random probability. This moment is the mathematical equivalent of creativity. The difference in the change of direction determines the outcome.

Creativity can have many more splits of direction than two, but two is an excellent starting point. Which of the two do you choose? It doesn't need to be random. If you have a goal, it might dictate the choice.

Wow. I think you're the first person I've seen to find a way to relate mathematics and creativity. My tutors tried by using x+y=z (or some other pseudo-algebraic equation) and telling me to treat the variables as nouns and the operators as verbs to construct a story. You can imagine how well that went.

I've never really studied fractal mathematics in depth, but this provides an interesting perspective. I will research it a bit more to improve my understanding. Doing a basic search, I found "Chaos: Making a New Science": Is that the book you're referring to? I'll look into it.

You are being creative right now. 

You need to understand that anything can be creative if you stretch your imagination to see.   I can make this paragraph as dull or interesting as my focus allows.   I have already captured your attention, I'll bet,  just by posing this idea to you.

You ARE creative.  We all are.  The trick is in appreciating that you already are.

If you want to use your creative juices in ways you feel you cannot, it is probably because you don't know why you don't know how to be creative as say an artist or a good writer.

But just writing this question on here and asking is being creative.  It sure beats trying to figure it out yourself when no answers are forthcoming. 

Not a bad video. A few too many of those popping up words and strange visuals, but good solid information.

Yep, that's it.

Another brilliant book is Arthur Koestler's "The Act of Creation."

Especially for you, the section on the scientist (one third of the book.)

Also recommend any of your choices by Edward de Bono.