I've found that there are no tricks. It's mostly just sit down and start working. It'll take about 5-10 minutes of steady concentration and suddenly I'll drop into the zone. There is no substitute for "just do it" as far as my personal makeup goes. I used to try all the various hack your mind stuff that comes out every few years. But when it came down to it there was no substitute for just sheer concentration on the task at hand.