Be religious about writing down what you're doing, make a habit of referring to this list when you find that you're bouncing around from task to task.

Sometimes I'll hit HN if I'm waiting for something to finish, and if I was in the middle of something complex I've needed to write down what I was doing, even if it was only for literally a minute.

Also, when incrementally learning something it can help. Writing down in your own words how something works can help you if you only have small chunks of time to learn something.