Being lovers without being friends.
If you don't know each other well and you are absolutely unaware of what matters to him or her, you might enjoy a month or two of good sex but then everything will be over – often without an apparent reason.

Not being honest and open about your true feelings, wishes, problems.
Hiding from problems can be no more than a temporary tactics. If you pretend that there are no problems, this leads only to one thing – the more you wait, the more serious the problems become. Patience is golden but not when there is a problem, which you and your beloved one have to solve. Hiding your true feelings is not a solution but most often people do it when they know there is only one solution – to separate – but they don't have the strength to do it.

Dependence on your partner.
While there are parasites just hook onto somebody to make their life easier (we can hardly call this love), normal grown up people also make a similar mistake – they expect the other person to establish their lives for them. The opposite pole is when you neglect everybody and everything else but the beloved one and you build your whole life around him or her. This makes you very, very dependent and when your relationship crashes or stalls, you are too tied to go.

The Fast Lane to True Love.
No matter if you are in a hurry or not, true love, unlike sexual attraction does not happen overnight. It takes time – months, years, decades. If your habit is either to start too fast, or to leave too soon, do not complain that true love misses you (or you miss it).

A hostage to first impressions.
Even if you judge quickly and generally your judgment is right, first impressions can be misleading. Always have a grain of doubt about the correctness of your first impressions – this will save you a lot of disappointment.

A relationship is the balance between romance and sex.
When you stumble in either direction – romance without sex or sex without romance – it is very painful to hit the ground when you fall down from the skies. A healthy relationship can't be based on sex (you can always get a hooker, if your hormones are disturbing you that much) only and it can't be merely platonic (even friends with benefits offers more).

Having not much in common.
Yes, the opposites attract each other but when you have more differences than similarities, don't count that you as a couple will have a combination of the virtues of both of you. For instance, if one of you is determined, while the other is more a slow thinker, this will make your relationship very difficult, when you have to make decisions as a couple.

Similarities with previous relationships.
When you start a new relationship, do not use it as a way to relive your lost love. Living in the past and not being able to forget an ex-lover can undermine even the strongest love. Many people will hardly be happy to be compared to your sweet ex who dumped you but whom you still love.

No clear idea of what you want in a relationship.
If you don't know what you want (whims excluded), do you think you will know how to get it and how to keep it for a long time? If you want affection, sex, security, faithfulness, or simply a devoted friend more than anything else, then sort your priorities and act accordingly.