Go to the options, set the Upload Slot Minimum to 1 (never increase it, it can cause lot's of problems) and set the Upload Slot Slot Maximum to 4 or 5, or even lower (I set it to 2).

Uploads will usually drop to 0k more seldom if you do so. One reason for 0k uploaders are hosts, that are disconnected without closing the socket due to a connection error, ISP connection reset, LimeWire is closed (- hey, that's a but indeed, LimeWire should close all sockets before exiting!!).