There is a great book on the market, called "Taking Charge of your Own Fertility"......and it is a super book that will tell you all the natural signs of ovulation, etc.
However, I will tell you the short version. It says to look for these signs, which form the word "SHOW" Each letter represents the following:
S = soft
H = high
O = open
W = wet
You will know you are ovulating when your cervix is really deep inside (high), when it is soft and squishy to the touch (almost like a squishy sponge) and when the opening feels very open (not as much as a fingertip, but almost), and when it is quite wet. By wet, I mean that after checking your cervix, when you pull your fingers out, you should be able to separate your fingers as far as they will go and the mucous on them will stretch, stretch, stretch and not break. It will be clear and have the consistency of a raw egg white.
Hope this helps.