I think this is the hardest part about doing this. But I try to find other productive things to do while things are compiling.

- Write code comments

- Write tests

- Have a separate code checkout where you can work on another feature.

- Research the next thing you're working on.

- Work on improving the build time, while it's building :)

It's hard to always be doing something, but if you consciously make an effort to do it then it can have a large impact.