E-mule is working in the same way like other file-sharing softwares : the more you give - the more you download.
all you need is allowing e-mule to upload at least as much as you download and share files that will interest other users.
you can also try to use some "booster" softwares, i didn't try it but you can try if you want. just Google "speed e-mule" or something.
good luck.