How to have good sex
The key to having good sex is communication - telling your partner what you like and what you don't like. Masturbation is a great way to learn what your likes and dislikes are, and it's important you pass this information on - if you're having bad sex and you don't tell your partner, they won't know they need to change.
Relaxing will help when you're having sex. Not only will you enjoy it more when you feel comfortable, but you're less likely to encounter problems like premature ejaculation (coming too early) or impotence (not being able to get or sustain an erection). Take your time and don't rush things - sex isn't all about getting to the end! If you're having intercourse, penetrating the vagina or anus will be much easier if you're both relaxed, and your bodies are highly turned on and ready.
Variety is the spice of life, and - if you want to - experimenting can help to keep your sex life fresh and exciting, particularly if you're in a long term relationship. It doesn't have to be anything kinky - just trying a new position or discussing a fantasy one of you has will help liven things up. Trying something new might actually help you improve your sex life - if for example you find that the missionary position doesn't provide much stimulation for the clitoris, try something new.
People seem to think that sex is all about penetration, and they forget that there are loads of other ways to give each other pleasure. Mutual masturbation or giving each other oral sex can be just as enjoyable when continued to orgasm. It's also important to remember that touching each other and playing with each others bodies, particularly the sensitive erogenous zones, can lead to better orgasms for all.