One way that I found very useful to increase my productivity is background thinking.  It is not usually what people can do just when they read it. Some self-training is required, though some people learned it instinctively.

The principle is: when you have something to think about, imagine that you put it like a mid-size closed box somewhere in your mind. May be on a shelf, or in the dark corner - depends on how you can imagine your mind. To me it usually a long room with lots of corners but never ending, completely dark. I can see a small portion of the room only because I have a small light. I walk through to put my box somewhere. When I finaly found a right corner, I know that "room" will do its magic: it will make content of the box cooked and transform from the problem to the solution. When it is ready, I usually find the box half-opened in my mind (like someone looked into it).

This "magic" works not only when you are awake but also when you are asleep. Just let yourself forget about this box for a while. Tell yourself several times very clearly: "I will remember about this problem in two days" and most likely solution will be ready in two days. If not, you can always extend to next period.

But make sure to remove the box from the mind  or you will end up in lots of old dusty empty boxes lying here and there. Keep you mind clean.