If you have files that refuse to download, chances are they are fake/spam files. Check them with
Bitzi Web Lookup before attempting to d/l. If there's nothing listed for it that's another sign that it's probably a fake. Bitzi also has magnet links that are sometimes useful in finding good files.
The files that have a lot of sources are mostly all fake though sometimes a good one will be mixed in. You have a better chance trying files with the least amount of hosts and a modem connection.
When searching for files vary your searches by using only the "keywords" and not the full title, also add the file extension to the end of the search(avi, mpg, ect).
New current/popular files are the hardest to find due to the large amount of fake/spam files being put on the network. Also they may not be available yet. It takes time for files to filter down through the file sharing community.
More info on fake files in this post:
Recognising fake files.
Tips on finding music here:
How to find music 
Hope this helps.