You don't have to play exactly as it says on the sheet music unless you are in a large group or orchestra, so just vary it a bit to give more feeling.
In addition learn the circle of 5ths so you can sort your own chord progressions.
To remember music learn 4 bars at a time until you cant get them wrong, then move on to the next 4 bars etc. until you can put it all together without needing the music.
Fake books are a good way to learn flexibility, as they just give you the basics thus allowing the player to improvise around them.

Bill