If you are trying to become pregnant, charting your ovulation is the most common way to predict when you are ovulating. Ovulating is the release of a mature egg. Calculating when this happens increases your chances of fertilizing that egg and becoming pregnant. Of course this is different for every woman, so keep that in mind.
Knowing and understanding your body is one of the most important parts of getting pregnant, especially if you are having difficulty getting pregnant. This could start with keeping track of your menstrual cycle. A menstrual cycle occurs every 21 to 35 days and lasts anywhere from 2 to 7 days. Ovulating then usually occurs 10-16 days before your menstrual cycle begins. Keeping track of when your menstrual cycle begins and ends for several months may be a good indicator if you have a regular menstrual cycle. If you have a normal/regular menstrual cycle, calculating when you ovulate may be a little easier.
Another thing to pay attention to is your cervical mucus–vaginal discharge. The amount, color, and texture of this discharge changes due to your hormones changing. Once your period ends, the discharge may look a little cloudy and thick. A few days leading up to ovulation, your discharge may change, becoming thinner and slippery. When (and if–it doesn’t happen to everyone) this happens those are your most fertile days. You’ll notice your discharge becoming thin and more clear.
Some women will have an increase in breast tenderness or sharp cramping pains while ovulating. Of course these are not really reliable signs of ovulation but knowing your body is extremely important. Keep track of all of the changes your are experiencing to “weed” anything out if necessary.
I would highly suggest keeping a journal or calendar of all of the above. Keep track of when your menstrual cycle starts and ends. Keep track of any changes in your vaginal discharge. Keep track of any body tenderness you may experience (whether it helps or not!). Some women will also keep track of their basal body temperature using a basal thermometer to check their temperature at the same time every day. An increase of .5 to 1.5 in temperature usually occurs when ovulating. There are also several ovulation calculators out there to help you if you need it. I really like one on thebump.com.