1.Put the item you want in the six slot in the item list.

2.Go to Virdian City and talk to the guy who shows you how to cath a weedle.

3.After watching him catch it fly to Cinnabar Island.

4.Surf on the right coast. After getting on your Pokemon just surf up or down, so it looks like your Pokemon is on half land and half water.

5.Wait until you see the Missingno, when you do, you can either run away from
it or you can kill it. When your away from him, look at your item screen and
next to the sixth item is a symbol where the number usually is. There is about
130-200 of that item now.
6.(Hint) A good way to use this trick is with rare candies, tm's, nuggets, or
Master Balls.

Free Coins:

1.While your in the casino with the slots in Celadon City, walk around while
repidadly pressing the A button. Do it all around the Casino and you should
get about 200+ coins.

Safari Pokemon on the Coast:
1.Go the the Safari Zone in Fuschia City and play in the Safari Zone until your time
runs out.

2.After you leave the Safari Zone and its building, fly to Cinnabar Island
and surf up and down the Coast.

3.As you surf up and down the coast, you will find the exact same Pokemon
that you saw in the same order from the Safari Zone.

Great Balls that work like MasterBalls

1.Throw a Great Ball at a Pokemon.
2.Press Up+B while he throws the Great Ball and it will catch almost any Pokemon.
Note:
You must time it just right to catch the Pokemon.