set the bobbin tenson first. when holding the thread, the bobbin in the case should slowly drop to your other hand, not stay in the air, or fall rapidly. turn the screw slightly each time you adjust.
Then adjust the top tension at least a half a turn each time. It is not like your domestic machine where you adjust a bit at a time. If there are loops on the back of your sample, tighten it more.
When you get it close, it does help to conceal those dots of top showing on the back if you use the same color top and bottom.
A problem on the back of the quilt, is a top tension problem. A problem on the top is a bobbin tension problem. If you set the bobbin first, then all your adjustments will be with the top.
This is an excellent video on needles, thread and tension for all brands of machines.
http://www.handiquilter.com/videos/?id=188