Rock Band 2

This can be done 2 ways as it says 25 hard challenges OR 10 expert challenges, not a mixture of both such as 20 hard and 5 expert..
These can be done a little easier if you are not up to the hard or expert difficulty by playing through a set list on an easier difficulty then on the last song switching to expert or hard. Whichever floats your boat.
You can if you have money for songs to download, there are a lot of songs easy that when you download a set or album of that artist you get a challenge too which could help you.
Finally if your having trouble with these alone you can also do them over xbox live or local co-op and be sure when your trying to do this if your switching over to a harder difficulty at the end that the last song you know you can pass at that difficulty since some songs can leave the hardest for last or may have the hardest right in the middle and the easiest last.