Spend time doing activities you both enjoy. Schedule regular dates with just the two of you so you can stay connected. Hang out together often and do things that reinforce your common interests.
Sometimes an affair starts with the simple act of a partner finding someone to listen to them. Don't let this happen to you. Pay attention when your partner wants to talk (or complain) about their day at work. Offer compassion when your partner is having problems with friends or family members. Be ready with a kind word when your significant other wants to vent. Part of good communication is simply acting as a sounding board. No one wants to feel ignored or uncared for.
Couples who try to avoid conflict by pretending things are fine are setting their relationships up to fail. If you have something on your mind, you must bring it to your partner's attention. Be kind and thoughtful when you talk about issues, just as you would when you were first dating. But be sure to talk about them.
As time goes on your partner will begin to know you better, but they'll never be able to do exactly what you want them to do without telling them. Don't get frustrated with your partner or assume that you're not compatible just because your partner doesn't sense every thought and feeling you have.
As you fall into a dating pattern you may begin to forgo the simple acts of kindness you did when you were a new couple. Appreciate your partner and think of them the way you did when you were first dating. Give them love notes here and there, hold the door for them, and say "thank you" when they do a household chore.
Imagine if your partner would be gone tomorrow, how would you feel? Treat each other as if your relationship is precious. It is.
Just as it's important to spend quality time building a friendship between the two of you, it's just as important to allow them time for friends, or to do solitary activities.
Don't let there be any grey area when it comes to cheating or emotional affairs. Make sure you both know what you'll tolerate in terms of fidelity and sharing. Know where the boundaries are, and obey them.