Like dramamon said, ovulation is a once in a month occurance. It is when one of your ovaries release an egg. The egg is only "alive" for up to 48 hours before it dies and is gotten rid off by the body through menstruation. It is a very short window in order to conceive. Ovulation occurs about 14 days before your period. If you happen to have a very regular cycle (the same amount of days month after month), it is fairly easy to "guess" the date of your ovulation. However, if you are like many other women, your cycle may be 28 days one month, and then 33 days the next, etc. This makes it trickier to predict the day of your ovulation.
That said, as a background... a man's sperm can live in a woman's body for up to 3-4 days, given the right condition. So if you have a guess on the week of your ovulation, you can start having sex a few days before and perhaps have sex every other day for the next week or so. This way, you will be bound to "hit" your ovulation.
Another, more effective method of knowing exactly when you've ovulated is through the use of Fertility Awareness Method (FAM). It involves taking your basal body temperature every morning (about the same time everyday) and charting it. You will find that your temperature is pretty constant throughout your cycle until the day of your ovulation. The day after your ovulation, your temperature will have a little bit of a spike. Your temperature will stay at this "high" spike until the day your period starts, at which point your temperature will go back down. This method alone is not as useful because by the time you see your temperature spike, it means you ovulated the day before. So most people, inlcluding me, use another method to go along with taking your temperature. You monitor your cervical fluid. After a woman's period, there are a few dry days where there is no cervical fluid present. After that your body starts to produce fluid and it will differ in consistency as you near your ovulation.
I hope that's not too much info. If you'd like to know more about FAM, I suggest looking to the book "Taking Charge of Your Fertility" by Toni Weschler. It is an excellent book and it has helped me get pregnant 2x very quickly. If you are coming off of any pill or other contraceptive, this may affect your ovulation. It is possible that you may not even ovulate for a month or longer after getting off. By charting, you will also know if you are indeed ovulating.
Anyway, good luck to you! I suggest taking prenatal vitamins now (my doctor ordered me to do the same). Also, your hubby's health is also important on this. Having a haitus on drinking, smoking, and other bad habits will probably also help in your efforts. A multivitamin for the hubby is also not a bad idea.