You must get used to your newly purchased piece of equipment. Strap on your harness, walk around, stand in front of the mirror, and get used to how it feels before you jump on your waiting partner. Make it a mutual event; let her help you into the harness. The trick is that the tighter it is the more control you will have, although there is no need to cut the blood circulation off.
Candles, soft music, and lots of foreplay are a necessity. Touch her and excite her, you need to get the juices running before penetration. It should be a joining of the bodies and a celebration of your love.
The controversial part is do you put a condom on or not? But if you do you would need to use a bit of lube, the more you use the more slippery and wet and so much more enjoyable.
Go slow and easy the first time no need to show how many movies you have watched. Angle your dildo upwards, not back toward her spine. Let your partner guide you in how fast, slow, deep, and for those who are adventurous rough.
Experiment with different positions. Old-fashioned missionary position allows for face-to-face intimacy and the most intimate of kissing. Doggy-style allows you to penetrate further inside her but this falls in more the quickie range.
Carry on touching and kissing, caress in the most intimate spots and love her.
Some couples can talk while making love, communication is good. Share what you like and how you like. Listen and pay attention to her body language.
Remember if you share any sex toy and use condoms, don’t use the same condom twice!