Baby-Boy-Girl: Naturally

Timing intercourse: Have intercourse the day of ovulation.

Timing intercourse correctly is the most important factor.
Learn to detect when you ovulate and practice until you're sure you understand your body's signals that ovulation is approaching.
The ideal time for intercourse is 12 hours before ovulation.
Have intercourse only once on the day of ovulation.
If you are tracking ovulation by the BBT method, time intercourse for the day of the "dip" in temperature before the BBT rise.
If you are tracking ovulation by the CM method, time intercourse as close as possible to the shift from peak mucus back to thicker, cloudier mucus.

Why is this important?

Conditions for conception are ideal on the day of ovulation, favoring the faster Y-sperm. The egg is released at ovulation and is waiting for the sperm, so the sperm don't use up their short lives waiting for the egg to show up. Also, the environment of the vagina becomes more hospitable to sperm at ovulation; the cervical fluid increases and becomes more slippery, making it easier for the sperm to swim, and also becomes more alkaline, helping the sperm to survive.

Intercourse and ejaculation are okay up until 4 to 5 days before ovulation, but after that point the father must avoid any ejaculation until the day of ovulation.
Always use a condom when you have intercourse, both before and after ovulation, to prevent the possibility of conceiving on days when it is more likely to have girl. (Except, of course, during your one attempt on the day of ovulation.)

Avoiding ejaculation allows a higher sperm count to build up. Higher sperm count is associated with more male offspring.

The father should make sure to avoid excessive heat around the scrotum, which can be caused by tight, hot clothing, or an overly hot workplace.
Choose boxers. Even close-fitting underwear can make the scrotum too warm by holding it too closely against the body.
No saunas, hot tubs, or scuba diving.
Bicycling has been linked to impotence and reduced sperm count, so while you are actively trying to conceive you may want to choose another sport.

The optimum temperature for sperm production is a little lower than body temperature, which is why a man's sperm factory is housed in a handy bag just outside the body -- the scrotum. If the temperature is too warm, sperm count for both X and Y sperm will be reduced, but the more fragile Y-sperm will perish first.

Illness can temporarily reduce sperm count, so if the father is sick you may want to delay your attempt until the following cycle.
Smoking, drug and alcohol use, and exposure to toxic chemicals, can all reduce sperm count.
Emotional stress is associated with lower sperm counts. You may want to check into relaxation techniques.
Regular exercise and maintaining a healthy weight are lifestyle changes that can improve sperm count.
Lack of certain vitamins and minerals can lower sperm count. You may want to try a nutritional supplement for enhancing male fertility
If you're worried that you may have a low sperm count, you can use an at-home semen analysis kit to check your sperm concentration.

Any form of stress, not just heat, can affect sperm production and lower sperm count.

The father can have a couple of cups of coffee (or other caffeinated drink) fifteen minutes to half an hour before intercourse.

Caffeine gives both types of sperm a boost, but the Y-sperm would get a little more of a boost.

The woman should try to have an orgasm during intercourse, ideally just before the man's. (If you don't, though, don't get too hung up about it.)

Female orgasm causes the cervical fluid to become even more plentiful and alkaline, and thus more hospitable to the sperm, which would again favor the faster swimming Y-sperm.