I love this game. It's a lot of fun and a lot of good exercise.
Your level is key to getting the best Pokemon offerings from the game and therefore XP is the most important component of the game. Quick tips for maximizing XP:
1. Go into cities with a lot of historical sites, monuments, etc. Work on getting something called a "Lucky Egg" at Pokestops. These lucky eggs will double your XP earnings for 30 minutes.
2. Time the use of your lucky eggs with the hatching of your Pokemon eggs, especially the 10 km hatchings. The experience associated with this will double from 1,000 to 2,000.
3. Evolve as many Pokemon as possible when your lucky egg is active. You can do this quickly with such Pokemon as Ratatas.
4. Catch all the Pokemon that come your way. Don't be selective. Each Pokemon allows you to evolve more and gain more experience (of course prioritize what you know you're close to evolving).
Tips for Egg hatching
-Use your permanent egg incubator for smaller distance eggs and your throw-away incubators for longer distances. Those will also be given to you at Pokest
ops so don't be sparing about this. You will get a lot of XP when these hatch.