In it for the Long Haul

For the long treks hunting pokemon and visiting pokestops and gyms, there are a few things you can do to get in the zone.
For one, you should activate battery saver mode in the settings menu. This will blank your screen while your phone is upside-down in your hand or pocket. If vibration is on, your phone will still vibrate when a pokemon enters your area (or vice versa.)

You also probably want to turn off the background music so it doesn't get repetitive and distracting.

Finally, you probably want to set your screen timeout to maximum. This way your screen won't turn off while you're hanging out in battery saver mode. You should be able to do this from your phone's settings menu.