Love relationships are uncertain endeavors, so you always need to be willing to risk. Nevertheless, I think you would have less problems if you got to know better the person you are interested in before you start a relationship with him. It's helpful to know what are his interests, character, his views on things, how he reacts when he's irritated or angry, etc. And for this, you need to spend quite some time with him, which means that you don't start the relationship straight away, and that you must have enough common interests to do activities together even though you're not in a relationship.

You don't have to know a guy for 5 years before going out with him, you could even go out from the first day on, but you must be aware that you need time to know a person, either before or during the relationship. But when you are in a relationship, you can't really look at other people, whereas if you are single, you can spend time with different people that may turn out to be interesting to you. Committing to someone you're not too enthusiastic about just to avoid being alone might be a bad choice, since you may miss a much more interesting person otherwise. Sometimes you need quite a while to understand that a certain person is not right for you. That's unpleasant but not a waste, since in the future you'll know that this type of person is not the one for you, and go for a better match.

To summarize: your relationships will improve when you'll learn to understand what qualities and flaws of a person work for you, and recognize those traits among the people you're interested in.