Are you guys not able to IP ban this guy? Anyway, I feel that, due to the specific forum, I should at least legitimately answer, even if it is a spambot. So, here it is:
You play the Pokémon games in whatever order you please. One group that follows after previous games is Gold/Silver/Crystal/HeartGold/SoulSilver, which take place a few years after Red/Green/Blue/Yellow/FireRed/LeafGreen, but they're still independent of each other to the point where it doesn't matter if you play them out of order. Another set like that is Pokémon Colosseum and Pokémon XD: Gale of Darkness, which are both for the GameCube and can still be considered independent of each other, even if they are more closely tied together. Another group like that is Black/White and Black 2/White 2, which, from what I've heard, are tied together closely enough that you need to play the first games first. If you want to extend this to the non-mainstream games, then all of the Pokémon Ranger games are technically sequential, but not so closely tied that you have to play them in order. The same can be said for the Pokémon Mystery Dungeon games. I don't know enough about the other Pokémon games to really say anything about them, aside from the fact that Puzzle League, both pinball games, Snap, Stadiums 1 and 2, and Battle Revolution are all standalone games.
Also, would somebody in staff please remove the signatures this guy has been adding as soon as someone replied to his posts?