I know that in many contests, sitting on a frequency and calling CQ is a very effective strategy to rack up points. However, during very popular contests it can be very difficult to find an open frequency. How can I find a frequency that I can use to call CQ during a busy contest?
One strategy is to camp a frequency starting before the contest. No, those QSOs don't count for the contest, but it lets you get into the rhythm of things and shake down any issues with your setup before the clock starts running. Lots of contesters do this and you might pick up some DX while running like that.
In multi-band contests, one strategy is to move down a little early, i.e., ahead of the pack, and stake out a spot. You give up a little in moving while the higher band is still productive, but you could get a choice spot for the next band and that should more than make up for it.
You can also use anything with a waterfall display to help you find open space. If you're set up for digital mode operation, you can run fldigi even for CW contests, use that to find the best "gap", and tune to it without actually using fldigi to transmit.