I had this problem forever until I figured this out...
When you are play long streaks of notes on the cymbal pads on expert, such as on songs like everlong and crazy train, try lowering the cymbal pads. It makes playing so much easier! When they are set lower, they don't have as much of a rebound, which causes you to often get out of rhythm, lose your place, or screw up. Try it, it really works!

Hey, droid here. Here are a few tips to help make a few hard songs a bit easier.
1: Hold down the fret button during a long string of the same notes. This can make tedious and repetitive songs such as Eye of the Tiger easier to play.

2: Try and find a pattern or rythym in each of the songs. This can be rather helpful in nailing those songs with long strings of notes.

3: Use the whammy whenever comfortable. You shouldn't use the whammy during short sustained notes or areas you are unfamiliar with. Trying to use it could possibly mess up your multiplier and reset it back to 0.

4: Use star power during the right time. It is recommended you try to activate star power when you have 4x already in your multiplier. This can allow you to use the full potential of the star power. It would also be helpful to use it during areas with many notes to get a maximum score.

5: Decide on a starting position. Some songs may not use certain notes very often, and this is common in hard and expert levels. One perfect example is once again Eye of the Tiger. Instead of starting with you index finger on the green fret, you should start with it on the red. This can allow easy access to the tricky jump from green to orange because your index finger is more agile and stronger than your pinky.