Your speed's always going to be a big factor! Also the connection type/speed of the host you're downloading from.
Try to download a file with multiple sources & as many stars as possible. Just stick to downloading one file at a time.

Often, using the All Types search will give you better search results & so more choices for downloading. Have a look at this thread, it has some tips
http://www.gnutellaforums.com/showth...764#post187764