If you want to have a really strong team to prepare for the Elite Four, and you have all three starter pokemon, you should have venusaur learn Frenzy Plant and SolarBeam, Charizard learn Blast Burn and Fire Blast, and Blastoise learn Hydro Cannon and Hydro Pump. Blast Burn, Hydro Cannon, and Frenzy Plant are like the fire, water, and grass versions of Hyper Beam and cause as much damage as Hyper Beam (not counting weaknesses and strengths).