When starting out playing pokemon with people online, I thought I knew a lot about pokemon. Yeah, right. There's a ton of things I didn't know, and a lot that I still don't. But the most important things for any newcomer to know, in my opinion, besides the very basic workings of battles and stats, are EVs and IVs. You'll hear a lot about them on here, and at first I was really confused. Here are some articles from Serebii.net that I feel are vital to maximizing your Shaywin experience.

Must-Reads for Pokemon Newcomers

Stats
Status Effects
Natures
Breeding
Effort Values "EVs"
Individual Values "IVs"
Shiny Pokemon

Of course, if you remember every little thing about every pokemon, you've either got an amazing memory or you have no life and spend your time memorizing every little detail about all 450+ pokemon. Look, I don't even know how many there are off the top of my head. xD That's why these links are useful.

Useful Resources

Serebii.net 4th Generation Pokedex
Smogon Strategy Pokedex
Type Matchup Chart
Veekun Breeding Chain Finder * sooo useful for those who want to breed egg-moved pokemon but don't want to spend the time figuring out what parents to get it from

And finally, pokemon sites that I enjoy visiting. I find it nice to be active on a variety of pokemon sites, because then you can find a wider variety of pokemon for trade and the like.

Starry's Favorite Sites

The Cave of Dragonflies *awesome site with a ton of information and fun things
Psypoke *Very informative and lots of useful tools
Global Trade Station Plus *just discovered this a few days ago, and it's really unique and looks to be a place I'll be visiting a lot
FriendCodes.com Pokemon Center *large active forum with lots of members

I feel as if this should be bumped. It's at the top but with all the new members coming in, I think it's worth a read for everyone who's new to competitive pokemon.