Open ports 6881-6889 on your router, or firewall. TCP connection. These are neccessary to connect to other peers. Also, if you are on an asymmetric connection (like most DSL and Cable) limit your upload speed, using a different client (personally I prefer Shad0ws
and limit your upload so it doesn't affect your download. For example, I can upload @ 40k~, but doing so kills my download. So I limit each torrent to 10k, since I usually have three open.