Supportive partner. Having a loving supportive partner who understands your needs and concerns is the best way. By making a safe atmosphere and knowing that whatever your concerns, your partner will listen, what can be a frightening experience for many can be a truly enjoyable one.
See a gynecologist. Gyn dr. Can tell you if your vaginal opening is large enough and even gently divide an occlusive or rigid hymen almost painlessly under local anesthesia. This should remove fear of pain. Birth control pill plus condom for your partner should remove any fear of std or pregnancy. Patient, loving partner plus lubricant, if necessary in a pleasant, private & romantic setting should remove fear.