Easy EXP

[Sephiroth]

Now, this isn't something you can regularly do, but it is a long term focus task.

When you have a common pokemon in your area, such as Pidgey for me, you capture TONS of them, but don't upgrade anything yet. After you have amassed a large collection of eggs for numerous creatures, you can activate a lucky egg for double EXP. At this point, you can evolve all of the pokemon you have been hording, and get some EASY levels.