When I was in university I had a serious problem with concentration and being "in-and-out" of the zone. So for two years I made an effort to have something chewing in my mouth(started with candies, then pen, and after a couple of unfortunate blasting incidents-coffee stirring rods) whenever I was 'in the zone' or about to be.
After a while, I've been conditioned to be "in the zone" on cue by chewing on a coffee stirring rod. it works about 50~70% of the time, and I have to be not tired at all. It's good to have it invoked on cue, though. I find drinking coffee in general not helping; caffeine is great in getting hufed up for a short duration, but I try not to consume more than two cups a week.
Addendum: A sad side-effect was that now I cannot seem to have meals without being mentally engaged - be it reading or conversing.
There's no reason to avoid caffeine. It's a very stress protective substance. Coffee with a little bit of sugar is a great way to sustain concentration far longer than you otherwise could. If one is adapted to it, it does not make one jittery.
Another lesser known chemical trick is aspirin. Aspirin boosts energy, mood, and concentration. Some days I down nearly three grams. I find it works synergistically with coffee.
One of my co-worker and one of my friends drink at least three cups of coffee in the morning alone to get the day started. The chemical tolerance they've built up scared me off.
After a while, I've been conditioned to be "in the zone" on cue by chewing on a coffee stirring rod. it works about 50~70% of the time, and I have to be not tired at all. It's good to have it invoked on cue, though. I find drinking coffee in general not helping; caffeine is great in getting hufed up for a short duration, but I try not to consume more than two cups a week.
Addendum: A sad side-effect was that now I cannot seem to have meals without being mentally engaged - be it reading or conversing.