There are many ways to improve the quality of your webcam broadcast.

First of all make sure you have a good internet connection with enough bandwidth. You can check how much bandwidth you are getting through e.g. www.speedtest.net.

To improve your quality even more you can use different kinds of stand alone apps such as

Wirecast
Vidblaster
Flash Media Live Encoder

Those different application provides you with more quality tweaking features. There are several tutorials on those application on their respective sites.

At last just some basic recomendations. Lowering the quality setting or video bitrate will improve video smoothness. If your picture quality is poor, you may consider investing in a higher quality camera. Also try adjusting your lighting. Digital cameras need a lot of light, and video will begin to appear grainy in dark conditions.