Hi Tom,
There are many techniques to make sure your bees use the Flow Frames. The most important thing I have read is that the colony needs to be strong before you add the Flow Super.
How long have you been keeping bees? Is your hive old, or new?
It would be good having a look at this thread:
You can also paint your frames in melted beeswax if you are worried and want the bees to start working in the Flow Frames fast - there are videos and instructions on the post above.
Good luck, and think positive 
Us hippies from the Northern Rivers, NSW would say - you attract what you think, so if you worry too much, the thing that you worry about the most will probably happen.
