While `zaphodiv' has covered most of the stuff, I'd like to add my penny's worth..
1) Low ID does not hurt.. just remember that if you have a Low ID, you cannot download from another Low ID user. Generally the %age of Low ID's are about 30%, so if you select files with lots of sharers, the Low ID is no problem.
2) Share.. suppose you want to download metal music, put decent metal music files in your shared folder.. This will help you earn credits from other sharers who are into metal music, chances are that they might be having the files you want, and if they upload your shared files, you get valuable credit points from them, which will help you to move up their `Q' faster.
3) The most vital point.. you might be having a 1gig download speed, but what if the files you are downloading is being uploaded by people who have low upload speed? Hence your download speed is directly controlled by the upload speed of the persons you are downloading from
4) Try to download a minimum of 5 files (max 25) at a time and see you speed rock.. do not try to download more than 25 files at a time or you might get blacklisted by the server