hi there.....this can be tough to pick sometimes as a lot of people realise when they start ttc.
You may see EWCM (egg white cervical mucous) just before ovulation which is a good indicator to ...get busy
But I found the best way to detect ovulation was to use OPK or (ovulation predictor kits). Not sure why they are called kits, they are just a test like a pregnancy test. You can get them cheaply on trademe...just search for ovulation tests
I ended up charting (taking daily temp) to be sure I was ovulating and when.....and lucky I did because when I thought I was ovulating I was wrong and we had been doing the business at all the wrong times.
Hope that helps a little and best of luck