When you first start dont worry too much about the speed or, as you say, you might end up slicing yourself or the strop.

Concentrate on getting a consistent stroke that keeps the blade flat on the strop the whole way and on making sure that you dont lift the blade at the end of the stroke. This can result in a rolled edge that will dull the razor.

The Wiki has more info on this as well:

Razor stropping - Straight Razor Place Wiki

Its really important to put the ground work in at the start because good stropping technique is crucial to maintaining your edge, so dont rush it! Take your time and get it right!

And most of all, have fun!