1. Don't be an open book
Before you open up your heart and become vulnerable, make sure that you know the person very well. Being an open book early on will always leave you in a place which can potentially damage you.
2. Observe the red flags
Do not ignore the little things that have been getting on your nerves. If he is flaking out, or tends to get upset easily, or even talk down to you- make sure to be attentive and not allow yourself to be disrespected.
3. Don't be too nice
Being over considerate and overly nice can sometimes backfire. This is especially true when you have the manipulative jerk that is looking to take as much as he can, and give little to nothing in return.