How to level up pokemon quicker?

Hello i got pokemon soul silver on the day it came out and im on the 8th gym. i need advise on how to level up quicker. here are my pokemon in my party and their attacks. Typhosion lvl 51- lava plume quick attack rollout and flamethrower. Gyarados lvl 30 bite dragon rage leer and twister. tentacruel lvl 22 wrap acid cut and bubblebeam koffing lvl 19 poison gas tackle selfdestruct andurance zubat lvl 18 fly wing attack astonish and bite slowpoke lvl 17 tackle surf water gun and confusion. please i need help!