Step 1: The Basics
Step 2: Singing
A warmer and more humid area to play loosens up your vocal cords and may allow you a greater range when singing.
You're 12 and a half, Jimmy. Put off singing until your voice doesn't crack.
Have a Drink
Taking a swig of water every so often helps, but a fruit-flavored juice is much better. If you don't have a juice drink at your house, you can take a bite of a juicy fruit.
Look, singing on Expert is no fun at all. You have to sing like a robot. I suggest staying low on your levels. Unless you're a competitive player and you don't want to have fun.
Step 3: Drumming
You don't have to slam the kick petal to get it to respond. Tread lightly on it so you can get those sections with quick bass beats.
Same thing here. Don't slam the pads as hard as you can. For one thing, it's really loud when you bang them like crazy. Also, putting a lot of weight behind the stick can slow you down, and you don't want that while playing on Expert.
The Guitar Hero World Tour is substantially better than the Rock Band ones. Even if you get the cymbal attachments for the Rock Band 2 drums, its unclear which one you're sposed to hit and it takes away from the experience when you hit the crash cymbal and you get a floor tom.
Step 4: Mic + Instrument
If you wanna play guitar or drums or bass and sing at the same time, I strongly suggest doing the song with just the vocals first. This helps familiarize yourself with the song so you can focus on the instrument.
A good mic stand for all three instruments would be one with a boom. That way, you have plenty of space in front of you, so you don't bump into the stand and knock it over. You can also clear the drums with the boom, so you don't have to do some crazy redneck rig with, like, a piece of Gorilla tape keeping the mic stuck to the ceiling, and place the drum under it so that it hangs there like one of those pull-down microphones that old-timey announcers used.