A lot of these are obvious but everyone should be aware of these tips.

First of all, identify if the lag is from your internet or from your computer being slow. To do this, run the game offline. If it lags then it is your computer. If not, you want to check that it is your internet that is the problem. Go online and start an online game by yourself. If it lags then your internet is indeed the problem.

Once you find the source of your lag, you are gonna want to get rid of it obviously. Here are some ways to reduce lag due to your internet:
-Close downloads, torrents, etc. (This applies for ALL members of your internet network!)
-Close any other programs that may be using the internet.
-Connect to a server that is closer to where you live. EGX = Northeast, Daroms = South, West Wonderland = West. There are international servers as well that you can find on the server list.
-If distance is the only issue, play p2p.

Here's a couple ways to reduce lag due to your computer:
-Close any programs that you don't have to be running.
-Lower your window resolution, and under no circumstances play with full screen. Make your resolution really tiny if you have to.

If anyone has anything to add feel free to contribute. Hopefully this will be helpful to those new to online gaming from your PC!

Sticky this Nintendude.

my game just slows down, the internet doesnt lag, when i run my game offline the game slows down as if it cant handle it what should i do nintendude?

How low is your resolution? Keep lowering it until it doesn't lag. If it still lags at a really small setting then your computer must be a piece of crap.

ahaha, its a brand new laptop, and its vista, i tried doing the trouble shooting thing but vista is just retarded. i'll work on it more later.

Yeah Vista is known to have issues with this. My guide has a link to a Vista troubleshooting guide.

for computer lag
killing explorer.exe would help. ctrl+shift+escape, click the processes tab, find explorer.exe, right click it and goto end process, click yes.

when you finish your game do ctrl+shift+escape, click the applications tab, click new task, type in explorer.exe and click okay.