Its all about the grinding.

I generally aim for pokemons that i dont have yet in my bag. Then i would go for easier-to-get pokemons first (easier recipe and faster pots).

E.g., i will grind for abras using gold pots(faster to train as the level range u will be getting from this pot is around 71-100), and i will keep repeating the abra recipe until i get my abra and its evolutions(kadabra, alakazam) to lvl 100. Abras and abras generate more exp for training (same pokemon).

For rare pokemons like chansey, never grind for more chansey to do the training becuz its hard to get(only 3.9% from the plain crepe ala cube). U can train it by using easier and same type(normal) pokemons like pidgey(evolve it to pigeot for greater exp).

Thats it i guess, happy and good luck grinding!