There are many different definitions of what constitutes great sex! For some people it's sex that is highly erotic, exciting, even dangerous. For others nothing is better than loving sex that involves closeness and communication. Some prefer the novelty of lots of different partners, others do not want to consider having sex outside of a committed, loving relationship.
Finding a loving, lifelong partner is an important life goal for many people. and for that relationship to remain vitally alive and satisfying, enjoyable sex is important. Some people find that sex helps them to feel close to their partner, while others require closeness before having sex.
One of the essentials of good sex is to understand the role sexual and non-sexual affection has in your relationship. It's important that you and your partner can be physically close and affectionate without either of you feeling pressured to have sex AND without fearing an attempt by either to initiate sex. This way you can establish closeness, love and reassurance, paving the way to having sex when you both feel like it.
Regardless of your style of sexual connection, when good sex is occurring it fits into place as one of life's pleasues, enhancing individual and relationship happiness. But if sex is not going well, it can feel like a huge problem. Sometimes partners have very different definitions of what constitutes good sex. You may want to discuss this together with a sex threapist to find ways to bridge the gap between you.
Being able to ask for what you want sexually is another important requirement. So too is accepting that you won't always get it! Partners cannot read each other's minds so each person needs to take responsibility to get their sexual wants and needs met. Sometimes this may mean you have to meet them yourself.
Giving feedback helps a lot. When someone else is touching you they cannot know what that feels like for you. You will need to tell them. If your feedback is negative give it gently and lovingly, with suggestions for what would be better.
Talk together, experiment together, read together, make sure you put time and energy into your sexual relationship (in proportion to all the other important things in your life) and it will reward you with lifelong pleasure and intimacy.