Knowing what you want before going into any relationship with anyone, what are your goals, where you are going in life and being open to compromise.
Once you know what you want then you are open to having a good relationship. Of course this is easier said than done, when you are dating in the beginning it is hard to come right out with your needs, for example, saying "look I want to fuck you senseless" on the first date. Of course you can't always say that. I read the body language and non verbal cues of my partner to see if he feels the same way just out of common courtesy, I am a bit old fashioned I guess. It takes time and patience to find out about the other partner and what his needs are but isn't that part of the mystery and fun of dating. And hey Rome wasn't built in a day. You also need to start off on the right foot, all cards on the table. It saves a lot of heartache later on down the track should relationship problems appear.
A good relationship is all about communication and we are all guilty of not always being open and honest with every partnership we have ever had. If you go into a relationship knowing what you want, 1/2 the battle is won. But upon saying that, you can only put in your 50% of the work in a relationship, your partner has to contribute the other 50%, any other combination means something is not working somewhere.