take a small notebook or sketchbook and put it in your bag or purse or whatever, whenever you get an idea ( which usually for me is whenever I have free time at work) you write it down and put it back into your bag, you cannot edit it, you can not rewrite it, you can build on it or write down a different variation of that idea, but you cannot scribble it out or white it out. Now, this can be an idea for a story, a funny line, a character, what have you as long as you think ( at the time) it's an idea you'd want to remember for later. Whenever you've got some down time or just have an insatiable urge to draw or write or whatever have you but don't have any ideas, pull out the book and read through the whole thing. You can get tons of ideas by building on the stuff, combining ideas, contrasting them, etc. it give you a secret inspiration stash that you always have on you that you can access whenever you want. You can even swap books when you fill it up and challenge friends to come up with something based on the ideas inside.