These apply if your a noob or a vet.
Always, always, always have some manner of stopping an outlaw or reviving yourself when you are below level 15 (which is most of the early missions).
When fighting tough bosses, like Groudon and the Luxio tribe, keep a Reviver Seed in your bag, and get as many team members as possible with you to the end. Save at the midpoint, and if you lose, turn off and keep going so you don't lose items.
Note certain suspicious things during the course of the game, as some secrets (im not spoiling the fun for you btw) will open up new areas, items, Pokemon, and all sorts of goodies.
Finally don't get frustrated. If you do, you WILL make mistakes and die. Be as systematic as possible. Especially in Monster Houses. If you go in there and act like a moron, you are guaranteed to die. Thats just all there is too it.
Hope this helped!
Added by: actionreplaymaster Apr 23rd 2008, ID#7345