Woo! Congrats!!!

My tips on changing a flat-
The front is pretty easy... don't worry about that too much.
The back- If you're worried about the cassette and derailleur, put your thumb on the upper guide wheel (assuming your bike is sitting upside down) and your fingers on the hinge-arm of the derailleur, so by squeezing thumb and fingers together you extend the derailleur arm up and away from the cassette. Doing this, you open up a good amt. of space to remove the cassette (having first opened the brakes accordingly and loosened the nuts holding the wheel in the dropout)

other than that, I have all the same difficulties everyone else has- I'm not godly like DebW, with her leverless flat-fixing.