This happens to me a lot. Many of my tricks are essentially created by combining two different ideas, theories, move, techniques, or methods each of which complements, or in some cases cancels, the other.
The onlly way I know of to think of these ideas is to keep a lot of individual ideas in your head, and think a lot.
To make this easier, when I read an interesting theoretical idea, I try to analyze exactly how or why it works, or what the most precise definition of the theoretical point is, or even just why exactly it interests me. This effort gives two rewards. First, this mental concentration helps to fix the idea in my long term memory. And second, because I remember it by way of its specific points, when I learn another idea that revolves around those same points, it'll remind me of the first one.
I've found that any time you can put two ideas together that have some unusual aspect in common, that axis of commonality can be used to make a deceptive trick. The more surprising or unusual the specific area of overlap is, the more deceptive.
Often you can find two ideas that multiply each other, rather than just adding to each other. That's another frequent avenue to a good trick.
Also, reread the Books of Wonder every year or so.