The Other Woman or Man
When you decide that you are going to cheat on your partner, you may already have a new person in mind, or you may be just looking for excitement outside the state of marriage. Before you begin to have an affair, you might want to consider the new lover's marital status as well; if you have little or no intention of leaving your spouse, dating a person who is also married but not planning to leave their spouse is optimal because you both have the same things to lose - which makes it easier for you to hide the affair. Because your lover does not want to get caught either, it makes it less of a chance that he or she will reveal the affair when the two of you call it quits. To spill the beans on you would be to spill them on herself or himself as well.
Keeping Emotions in Check
One thing that you need to do when having an affair to avoid getting caught is to keep your emotions in check. Avoid becoming too emotionally attached to your lover or falling in love with the other woman or man can cause you to put your marriage in jeopardy. Remember what you began the affair for in the first place, and stick to that mindset. It certainly wasn't because you wanted to actually love another woman or man - you just wanted to fill a void in your life or in your sex life.
Stay Out of Public View
No matter how small you feel in a big city, there is always the chance of being discovered by someone who knows your wife or husband, even if you don't know that this person knows you or knows your wife. Many people who get caught cheating were exposed by someone who knew someone who knew someone's cousin who knew your wife or husband, or so on. People love to gossip, and many people will tell all when it comes to exposing a cheating spouse because of their high moral standards and affections for your spouse.
Hide (or Destroy) Evidence of the Affair
While only an idiot would keep physical evidence of an affair, like a motel receipt, for instance, don't forget any digital evidence that you may have - such as text messages, email messages, and dialed numbers in your 'sent' list. Avoid staying on the computer for hours after your spouse has gone to bed for the night. And don't feel secure just because you have a password-protected computer that no one will see those nudie pictures your mistress sent; a technologically savvy wife can install a program on your home network that will let her take screen snaps of your activity without you ever knowing it.
In sum, if you don't cover your tracks when having an affair, you will eventually get caught.