There are a few possibilities:

1. Money (buy Incense, Lures, Lucky Eggs = win)
2. A lot of time (just do a lot of stuff)
3. Saved Lucky Eggs for mass evolving a full Pokémon zoo. (This method nets you about 30k XP per egg/30 min easily, a lot more if you prepared it properly.)
4. Cheating

There are a few possibilities:

1. Money (buy Incense, Lures, Lucky Eggs = win)
2. A lot of time (just do a lot of stuff)
3. Saved Lucky Eggs for mass evolving a full Pokémon zoo. (This method nets you about 60k XP per egg/30 min easily, more if you prepared it properly.)
4. Cheating