If you have used CLS, try off camera for portraits, make sure to bounce if you have low white ceilings, or white walls. CLS is a big feature, take tests using different zoom and power settings, do some DIY light modifier stuff. Check strobist, have fun.
begin with Strobist 101 and work your way through and then do the 200 level.
Do lots of reading, join the CLS page on flickr and have a look at shots. From the strobist stuff you should be able to begin to reverse engineer a lot of shots and understand how they were done. You can then start to engineer your own using your creativity.