Make sure he or she respects your decision. Keep your life lively. Put your thoughts and energy into something you enjoy, something productive. Think about where you want to be in five or ten years, and work on ways to get what you want. Together, you might spot trouble coming before it arrives.
Time is the best test of a relationship.
See what happens when you hold off having sexual intercourse. In the meantime, make yourself happy, have a good life, find someone to love who loves you back. That's the best part of being smart about sex.