Getting pregnant is all about timing. Most women ovulate about once every 28 days. You can only get pregnant for a short window of time during those 28 days. Once the egg is released it will only last a few days before you can no longer get pregnant. Most of the time women get pregnant when they have intercourse on the day they ovulate or the day before. You can get pregnant if you have intercourse in the days before you ovulate because sperm can live for a week or so, and you can get pregnant for a day or two after you ovulate. So the point is that you need to know when you are ovulating in order to know when the best time to have intercourse is.
Most women ovulate around the middle of their cycle but this can vary greatly (as can the total span of their cycles - not all are 28 days). There are other ways, however, that allow you to discover or at least estimate the time of ovulation. One way is to use an ovulation kit. It is very easy to use. You start using it right around the earliest time that you believe you will ovulate, usually a few days before the middle of your cycle. The kit will tell you exactly what day to start on based upon your cycle length. It is a urine test, and the result will show up in just a few minutes. Once you determine that you are ovulating, you should have intercourse in order to increase your chances of getting pregnant.
Ovulation kits can be pricey and you may need a new one for each cycle. Another method that is a little more difficult is to take your temperature during your cycle. There are subtle temperature changes that indicate ovulation. This can give you an idea of when you are ovulating, but you will need to be careful because the temperature changes are so slight that you may miss them if you do not know exactly what you are looking for.
Most women will get pregnant eventually. If month after month passes and you still have not had luck, you may want to consult a doctor who can test to see if there are any underlying problems as well as increase your chances of getting pregnant with medication.