I have a bunch of tips about scanning film on my web site. Perhaps some of them will be of use to you.
Just follow the tips link on the home page. The biggest thing is to use good scanning software. Many of the choices that come with scanners are designed for ease of use, rather than optimum quality. I like Vuescan from Hamrick.com, but there are others.
If you have an expert or manual mode in the software then try that and set it so that you don't clip either the shadows or highlights.
If you have specific questions, I'll be happy to try and answer them.