Ok, I have a 5 Pokemon team (and Useless HM user). But they are all in the 36-40 range. I have all 8 badges, and an currently in Kanto on the way to the Pokemon League, but I want to level my Pokemon up before even attempting to take on the E4. Does anyone have any tips and/or areas to quickly train? (Yes I know it's pathetic to ask for help in a Pokemon games single story, but I'm lazy and usually only use 1-2 Pokemon though the whole game until Victory Road)

My team.
Milktank
Haunter
Pikachu
Togetic
Feraligator
Quasigire/Rattata (HM Users)