Go to the toughest area you can think of, and train there (or fight the newest trainers), preferably near a pokecenter, unless you are fully stocked with items.
If you are talking about leveling up a Pokemon that is considerably weaker than you others, put the lil runt in the top slot in the menu screen and if he can't beat that Pokemon, switch him out for the next weakest one, so that your lineup is as balanced as possible. The fastest way is to fight the toughest trainers with your weakest out first, and switch out for one you know can win, so that they can split the xp. One more thing, if the replacement can't win, and you have to replace that one too, fainted or not, the weakest one will have to settle for 1/3 of the xp if the first two survived their battle. However, if the first one was only replaced once, and the replacement died, the first one can get all of the xp if he can pull of a win, and it doesn't matter how many items you give him. Eventually, you want the runt to be able to handle his own, or at least be able to attack and take a couple of hits without taking a dirt nap, though he doesn't get any more xp by taking a hit as he does just by being switched out. And yeah, during a battle, if you switch Pokemon before the last one sees the new one, the last one won't get xp, because both Pokemon who fight have to see each other to get xp at all.
Also, give your Pokemon items that either increase their elemental attacks (nevermeltice for instance) or speed (quick claw) or heal their status (burnt berry), or replenish their hp automatically (normal, super or hyper potions, or any water, pop, or lemonade). If they hold items, and if you use items regularly on them right when they need them, in battle or in field, they will like you, and will have better stats overall, including health points, speed, vitality, defense, and everything else, when they level up. Hair cuts help mood too, especially the better one, who is easy to tell by talking to both of them, though they don't show up on the same day.
Oh yeah, if you check their menu icons, you can see how much they move next to their names/hp and the faster they move in the menu screen the better mood they will be in, and yes, some Pokemon do evolve based on mood (like evee who not only can evolve through mood but mood and time of day too, to produce an umbreon in the night or a espeon during day). It also helps if you check the statistics of all of the Pokemon you get/catch as the stats are random, and if you can restart the game, for the EXTREMELY RARE ONES ONLY (like the 3 starters), you can get the one you want and maybe better stats than the one the first try gave. All the wild ones can be caught over and over, with the exception of a few, and you can choose which is better, and then let one go or keep hunting.
And if your Pokemon is a hatched Pokemon like a level 1 topepi give it the xp share to hold it will get half of the xp given.
Or you could just use rare candies.
see How get bicycle in Pokemon leaf green?
Charizard does not get fire blast in Pokemon red, his last move he gets is fire spin on level 55, the only way that i know of to get fire blast is by defeating the gym leader, Blaine on Cinnibar Island.
The best way to level up pidgeotto is to have the move quick attack and take him into diglett cave, just run around and use quick attack.
There's no TM dive in pokemon fire red but there is in emerald, saphirre and ruby. But the way is to level up pokemon (seel level 41,dewgong level 45) to get TM dive (in firered).
The best way to get Dragonair in Leaf Green or Fire Red is to envolve it from Dratini. You can get Dratini in The Game Corner in Celadon City ( The city where you battle with the GYM 4 Erika Grass TYPE).
use good Pokemon that's the only way
use cheat codes
see How get bicycle in Pokemon leaf green?
Pidgey evolves on level 18 on Fire Red. The best way to get it to evolve is to feed it rare candies.
Charizard does not get fire blast in Pokemon red, his last move he gets is fire spin on level 55, the only way that i know of to get fire blast is by defeating the gym leader, Blaine on Cinnibar Island.
There is no "Easy Way".....
train all of them they are all useful in their own little way
The best way to level up pidgeotto is to have the move quick attack and take him into diglett cave, just run around and use quick attack.
There is no sure way to defeat them at all , just have some good level Pokemon , and a range from Ice , Electric , Ghost , Grass , Fire , Ground and normal , and you will win that way
If you have a ditto,put ditto with your other Pokemon.Then you will get a egg.If you don't have a ditto,You can migrate one from a Pokemon fire red.
Lighters or matches.
there is no easy way to get to level 100 just stock up on joy seeds until you have enough for all your pokemon or just the pokemon you want to be at level 100.