Orianna
I'd wing it when you start unless you have a very irregular or long cycle. Not sure what you are doing timing wise - but friends of mine with no fertility problems just go like rabbits from the end of their AF for about two weeks. It worked for them almost straight away. Others say to BD every second day for the middle two weeks of your 28 day cycle.

If on the other hand you have irregular cycles - why not try temping. It teaches you heaps about what's happening.