Get Bulbasaur, Charmander, and Squirtle
In order to get Bulbasaur, train Pikachu until he is super happy and jumps up and down when you speak to him. Then in Cerulean City, go to the house with Melanie in it and she will give you her bulbasaur. To get Charmander, simply beat Nugget Bridge. Go north and there will be a ledge with a boy on it. He will give you Charmander as long as you promise to take care of it. Finally, to get Squirtle, beat Lt. Surge. After obtaining the Thunder Badge from him, speak to Officer Jenny outside and she will give you Squirtle.

Clone a pokemon
1.Hook up with a game link cable to your friends game to trade.
2.If 1 person has a pokemon that you want do this.
3.The 1 that doesn't have the rare pokemon trade a rattata.
4.When the trade is almost done the person who originally had the strong or rare pokemon when the screen says waiting turn your gameboy off before it says "trade complete".
5.Then the person with their gameboy on waits till it says"trade complete" and then turns their gameboy off.
6.When you turn your gameboys back on you should both have the rare or strong pokemon and the common pokemon should be gone.

Catch Pokemon Easily
This trick allows you to fight and catch the Pokemon easily with any kind of ball.
1.Get into a battle with any Pokemon.
2.Use a ball on them. Any kind of ball will work. If you have difficulty using normal Poke balls, try more powerful ones to increase your chances even more.
3.As soon as you see the ball explode, press and hold the B Button. The timing for this is very important. You must press B just as the ball explodes, which can be difficult. 4.After the ball wobbles for the second time, release the B Button and you have them.
*Note:This trick will not work every time, but it will increase your chances of catching them. It is not necessary to do any damage to them, but some Pokemon, like Mewtwo and Zapdos, will have to be put to sleep before the ball will hit them.

Tighter Pokeball
Throw a Pokeball and immediately hold A+B when it closes.It should get a better chance to catch a Pokemon.

*Note*
ALL codes I put on my website I have tested on my own versions of pokemon.
All are legitimate codes.