fight all the trainers who use Ground Pokemon. Water Pokemon are the best here. Leader of team rocket is the boss here and uses his Rhydon lv55, Nidoqueen lv53, Nidoking lv55, Persian lv53 and Dugtrio lv50.

Once you win, all Pokemon will obey you. Now, go up Route 22. Here you will fight Gary who will have all 6 of his Pokemon. Use each of your Pokemon against each of his Pokemon to find who are the best against his types. He uses Sandslash, lv47, Exeggcute lv45, Cloyster lv45, Magneton lv37, Kadabra lv50 and his evolved Eevee lv53.

Now, go to Victory road where you will have to push boulders to open doors to get out. Battle all the trainers and stay for a while until all your Pokemon are L60. On the first section push the boulder on to the plate to open the door. Past the door are 2 trainers you'll also find out that this path looks like a J. On the right side you can push a boulder to reveal one of two item balls. Push the boulder to the left to get a TM sky attack or push the boulder north to get a rare candy. On the 3rd section is a boulder over a hole push it down and follow it. Push the boulder to the left to open the final door.

To get Moltres, on the 3rd section go up the ladder near the plate. There's a trainer and a bird, SAVE FIRST! If you make it faint you will not have another chance.

The reason why I've said lv60 is your Pokemon will grow faster when fighting the Elite Four and it's more fun then spending hours raising levels slowly. Spend all your money on Revives, Hyper Potions, Full heals and Recovers so that if you lose you won't lose all your hard earned money.

Here are what skills my Pokemon know:
Dragonite: Thunderbolt, Surf, Blizzard, Hyper Beam
Pikachu: Thunder, Thunderbolt, Flash, Quick attack
Charizard: Strength, Flamethrower, Fire blast, Slash
Pidgeot: Wing Attack, Swift, Quick Attack, Fly
Victreebel: Solar Beam, Vine Whip, Sleep Powder, Cut
Gyarados: Surf, Dragon Rage, Hyper Beam, Bite

Here are the elite four and Gary.
Lorelei:
Dewgong: use grass or Pikachu
Cloyster: use grass or Pikachu
Slowbro: use grass or Pikachu
Jynx: use fire or Pikachu
Lapras: use Pikachu
Bruno:
Onix: use water or grass
Hitmonchan: use flying or psychic
Hitmonlee: use flying or psychic
Onix: use water or grass
Machamp: use flying or psychic
Agatha:
Gengar: use dragon, flying, ground, or psychic
Arbok: use flying, ground, or psychic
Haunter: use flying, ground, or psychic
Golbat: use psychic or Pikachu
Gengar; use ground, psychic, or Pikachu
By now your Pokemon levels should have gone up by about one each. Heal all your Pokemon and put Pikachu at the top.
Lance:
Gyarados: use Pikachu
Dragonair: use ice or Pikachu
Dragonair: use ice or Pikachu
Aerodactyl: use ice or Pikachu
Dragonite: use ice or dragon
Gary
Sandslash: use grass or water
Alakazam: use Pikachu
Magneton: use grass or ground
Ninetales: use water or ground
Exeggutor: use fire
Cloyster: use Pikachu
Jolteon: use Pikachu or grass or ground
or
Vaporeon: use grass or Pikachu
or
Flareon: use water

Well done! Now all you need to do is get Zapdos from power plant, Moltres from Victory road and Mewtwo from the unknown dungeon in cerulean city. Keep fighting the Elite four to get your Pokemon to L80. Then challenge a friend to a Pokemon match. You will probably win. In the unknown dungeon you will find very high level Pokemon like:

Golbat: levels from L50 to L59. They give over 1,000 exp. Points every time!
Weepinbell: these are rare but are great grass type Pokemon.
Gloom: same as Weepinbell
Rhyhorn: catch, as these are powerful
Rhydon: levels from L58 to L62 they give about 1,800 exp. Points
Chansey: very hard to find and catch they are on the bottom floor and have over 500 hp. They give over 2,000 exp. Points, but try to catch one.
Ditto: these aren't worth fighting as they give about 600 exp. Points. Watch out, they transform.
Graveler: don't battle until you can defeat them in one move, as they will use explosion!
Lickitung: another rare Pokemon. They don't give much exp. Points so just catch one and then leave them alone
Parasect: a nice Pokemon to add to your collection, but has a high defense
Venomoth: only gives 1,000 exp. points
Seaking and Goldeen: you need a rod, Seaking gives about 1,000 exp. Points

(I know about this because I've spent over 10 hours leveling up my Pokemon from all level 58to level 66. I don't have any thing better to do I guess)