Hey welcome man!   
Some tips I have:   
Don't evolve till extremely high levels. Easy EXP. 
So I wont evolve my gastly till  level 98. 
I level it up to 90, then I buy rare candies and level it up to 98, evolve to haunter. Then trade evolve it to gengar. :) 
Fight every NPC.   
Good luck! PM me if you need anything