1. Learn to be dependent upon yourself.
In order to let go of insecurity, you have to learn to depend on yourself, not a partner. Love isn't about leaning on someone for support all the time. Learn to stand on your own and you'll feel much less insecure.
2. Let go of your paranoia.
Most of the time, paranoia is based on nothing. Yeah, your partner will be talking to their ideal sex sometimes. They work with them, they go to school with them, they're friends with them.
If you can't trust your partner to be around them on their own, you aren't ready for a relationship.
3. Don't see things in black and white.
It's not always yes or no, good or bad. You can't see things in black and white like that. When you do, fights happen. When fights happen, insecurities arise. Be flexible. Don't point fingers. The truth is somewhere in the middle.
4. Leave your baggage behind.
The past is the past. You have to learn to let it go. If you keep carrying around your baggage, it's going to weigh you down and keep you feeling insecure.
5. Don't psych yourself out.
If you have a concern about something, let your partner know. There's no harm in that. If you don't, you're going to psych yourself out about it which leads to insecurity. Make sure your worries don't exist solely in your head.
6. Remember, it isn't all about you.
It's hard not to think the world revolves around you, but it doesn't. Once you realize your relationship isn't about you but us, you're going to be way better off.