I've been doing it for about a year. My top speed so far is 130mph.

I can tell you that it's much easier to do after you've actually seen someone do it in real life. I struggled for a while at my particular flying spot until I was able to see someone else do it (turned out my circle was all wrong).

This site has some good tips to get you started:

http://www.thehelix.com/soaring/articles.htm