Deb, you'll find HEAPS of varied information out there on the net but I think the best way is to actually just do it and 'feel' your way LOL. It'll probably take a cycle or 2 for you to start to recognise the changes but you'll soon be able to tell what your cervix is doing.

I found doing it at the same time each day worked best. You'll be able to tell how high your cervix is by how far you have to reach to get to it. You'll also be able to tell if it's open or not as if it's open you may be able to fit the tip of your finger in and at other times not so much. When you O your cervix will be high and open.

HTH!

ETA: Oh yeah and how soft/hard it is too - around O time it'll be much softer, usually described as being like when you touch your lip. Other times it'll be harder like the tip of your nose.