If you haven't tried sitting with a group, I highly suggest it. I find it much easier to focus, and there is more accountability so you can't get pulled away inside your own thoughts, then suddenly open your eyes and say, "I've got too much to do!" No, it's easier to refocus and sit until the end.

Also, I find guided meditation groups really nice. I'm a beginner, so it's great to have someone helping me along.