Many STDs happen because a barrier-a condom for the penis, or a film for the genitals of women- breaks. Plus, there are other things to consider, like comfort, transmission of sensations, and the possibility of allergic reactions. There are some simple things you and your partner can do to minimize these problems, and maybe laugh a bit at some of them.
What makes a good barrier?
A good barrier is one that covers the area, plus a margin for slippage. This is why condoms cover the entire penis, not just the tip: it would be difficult to keep it in place! The best barrier – other than not having sex at all – will prevent bacteria, microbes, viruses and mites from coming into contact with your partner's skin. Any openings, including unexpected ones, will open the possibility of infection.
You need to practice using the barriers before having sex. Being low-cost, and now available in both male and female models, condoms are a great place to start. By checking closely, a lubricant can be used that will not harm the condoms. If used on the skin before the condom is applied, this will help in transferring sensations to the penis. I suggest practice here: trying to apply a condom to a slippery penis is not something that can be done easily if you are nearly ready to have sex.
Making sure that the condom- for either of you- is on well before sex takes place is one of the steps that is skipped. The condom needs to be fully unrolled, which can be done well before any genital contact takes place. Using a lubricant and unrolling the condom should be incorporated into the act near the beginning- possibly being used as part of foreplay.
Pregnancy and STD protection
There is no way a barrier that stops STDs can allow you to become pregnant. This is a consideration for some women. Those in abusive relationships may have their partner refuse to use a condom, or will get a non-barrier contraception (like an IUD) that will avoid the pregnancy, but still allow for STD infection.
The problem with the female condom right now is two-fold: the cost and the need to replace after each sex act (like a male condom). Plus, some females make have problems inserting these, or think that a spermicide will prevent STD. These are dangerous problems. A condom that slips out of place will not protect, and there is no evidence that any spermicide will stop any of the STDs.
Alternatives to latex
The most effective condoms are latex. This, however, is something that people may be allergic to, anything from rashes to causing death. The new technologies have made alternatives available, one of them being a polyisoprene compound that is very similar to latex, but with the protein removed that causes the allergic reaction. These new products have some downsides, and you need to check carefully before use.