Ok, I have seen many fails.
So here is the advice that works for alot of people!
Step 1: Make one room and your sprites and the interface.
Step 2: Start programming, make the online stuff.
Step 3: Make it public beta (demo/trial) and finish the rest of the game.
Step 4: Finish the game while thousands join your forum.( Maybe not "thousands" but alot
)
Four little steps! And to start you off -
http://smartfoxserver.com(I got the flash's)