I would suggest that you stop trying. No kidding, trying focuses all your mental energy into efficient paths of thought -- that you're already familiar with. You need to let your mind wander off in unexplored directions. Creativity happens, you don't "do" it.
Yes I'm exaggerating. Many writers, in particular, make writing a regular day job and they just sit there 8-5 M-F and create words. But if you were that kind of person you'd probably know it by now.
And just because "your field" is mathematics (not proofreading as Blackie so kindly pointed out),

that doesn't mean that your brilliant ideas will occur in that discipline. It's quite possible that the parts of your mind that are not so well developed and organized and compartmentalized will give rise to some creative thoughts for the very reason that chaos and free association
may act as a catalyst.
Lots of people are really good at one thing and make a nice living at it, but when they go home at night they play the clarinet or do embroidery or invent tools.
For many people, the reward of creativity is the satisfaction of having done whatever you did, not necessarily the recognition by others or (you know what I'm going to say next don't you) money.
As for "creativity techniques," I would concentrate on more general mind-stretching exercises. You're at a perfect age to take up TM (transcendental meditation) or whatever kind of mediation appeals to you. Most of us math nerds could stand to completely clear our minds for a little while every day or two. Your brain is like a muscle, it needs to relax. I have a friend who took up TM as an adult, then suddenly when he was in his 50s he was struck with inspiration, sat down, and wrote a really good novel.
If meditation just doesn't appeal to you, spend time listening to instrumental music, hanging with your pets, or doing something that takes your attention away from your mind so that it can go off on its own adventures unencumbered by your detailed directions.
This is one of those things where you have to put up with some really paradoxical advice: Don't try so hard!
Good luck.
Oh, and don't forget that Prof. Nash was certifiably nuts. That's a heavy price to pay for creativity, and it's not guaranteed to work!