Without a doubt, the best way to protect yourself against HIV infection is to abstain from sexual contact altogether as well as avoiding other means of HIV transmission (needles, transfusions, etc.). To be clear on what "abstinence" really means, CDC has prepared a fact sheet sorting this all out for you.
Review Fact Sheet on Abstinence, and what it means

Statistics show that the majority of college students have already had their first sexual experience before reaching college and that they continue to engage in sexual activity while in college. Thus, for most students, it is important that they understand how to practice safe sex. For most, that means using a condom or other barrier method (See Dental Dams) to prevent both the risk of pregnancy and of disease transmission.

"Isn't it ironic that in this day of mindboggling technology, the most effective device to prevent the spread of AIDS is almost as old as civilization itself: the condom."

The correct and consistent use of latex condoms during sexual intercourse--vaginal, anal, or oral--can greatly reduce a person's risk of acquiring or transmitting STDs, including HIV infection.

In fact, recent studies provide compelling evidence that latex condoms are highly effective in protecting against HIV infection when used for every act of intercourse.

This protection is most evident from studies of couples in which one member is infected with HIV and the other is not, i.e., "discordant couples." In a 2-year study of discordant couples in Europe, among 124 couples who reported consistent use of latex condoms, none of the uninfected partners became infected. In contrast, among the 121 couples who used condoms inconsistently, 12 (10%) of the uninfected partners became infected.

Use Condoms Correctly !!!

Condoms must be used consistently and correctly to provide maximum protection. Consistent use means using a condom with each act of intercourse. Correct condom use includes all of the following steps:

• Use a new condom for each act of vaginal, anal, or oral intercourse.
• Put on the condom as soon as erection occurs and before any vaginal, anal, or oral contact with the penis.
• Hold the tip of the condom and unroll it onto the erect penis, leaving space at the tip of the condom, yet ensuring that no air is trapped in the condom's tip.
• Adequate lubrication is important to prevent condom breakage, but use only water-based lubricants, such as glycerine or lubricating jellies (which can be purchased at any pharmacy). Oil-based lubricants, such as petroleum jelly, cold cream, hand lotion, or baby oil, can weaken the condom.
• Withdraw from the partner immediately after ejaculation, holding the condom firmly to the base of the penis to keep it from slipping off.

Is there a female condom?

Yes.  Research indicates that male latex condoms seem to provide better protection against pregnancy and sexually transmitted diseases (STDs). However, if a male condom cannot be used, a female condom is the next best choice for protection. Male and female condoms should not be used together. Additional protection may also be provided by using a spermicide inside the condom in case it leaks or slips. Frequent spermicide use on the outside of the condom, for example more than every other day, is not advised because it can cause irritation, which may increase the risk of infection. Female condoms are available in drug stores, some community health centers, and some AIDS service organizations.

Can other birth control methods reduce the risk if HIV infection?

No. Birth control pills, Norplant, Depo-Provera, IUD or any other birth control method that does not keep blood, semen or vaginal secretions out of the body DOES NOT provide protection against HIV.

View a Movie on How To Put On a Condom

Watch this QuickTime movie
as Dr. Marian E. Dunn demonstrates the correct way to put on a condom.
N.B.: This [2.7M] video clip shows a realistic plastic model of a penis.

For more information on the proper use of condoms, visit safersex.org