1. Be realistic. This person hasn't changed in a week, two months, or a few years to the point that everything that was or still is wrong with him or her is completely removed. There will be some things that you still don't like about an ex that will show up sooner or later. Think about not only the good, but the bad too. List those issues and let them help you stay guarded with this person.
2. Fight the temptation to have sex. Romance and sexual intimacy doesn't heal, but enhances healthy, functional relationships. If there is dysfunction evident in any relationship, sex will just further complicate matters. Using physical romance to heal is like putting a band-aid on a broken bone. Put off talk about sex with an ex (you already know what it's like with him or her) and redirect your focus on those unresolved issues such as: the apologies you never received, lack of emotional support, cheating, lying, stealing, etc. whatever helped break you both up.
3. Stop lying to yourself. Until you face what you did to enable problems in the relationship, you will find yourself breaking every promise you told yourself you wouldn't do all over again. So be honest and do what you can to make past wrongs right.
4. Avoid moving in together especially to save money. Finances aren't nearly as important as inviting someone back into your life that could potentially wreck havoc on it. Slow down with the plans to cohabitate and the reasons why you should do it now rather than later. As soon as you open those doors, you will be opening yourself up to additional stress whether you choose to believe it or not. Cooking, cleaning, possible pregnancy, talk of marriage, in-laws, guests, respecting one's space, and more will still be topics of discussion.
5. Don't enable dysfunction. When those signs of control, denying, lying, blaming, etc. show back up again, it is safe to say you need to keep an ex at a distance. He or she might smile, joke or distract you from their true colors coming to the surface again. Don't fall for the tricks. State what you will not tolerate and create some distance so that you can carefully ponder whether getting back with an ex is indeed the right thing to do.
6. Don't share your personal feelings and experiences about your dates to the ex. Making a former lover jealous might bring some satisfaction to some people, but it is never a good idea if you one day hope to get back together with an ex.
When you know your worth and have a love for self, you will not tolerate anyone including an ex overstepping their boundaries in your life. You won't be nervous, fearful, or stressed about stating how you feel, because you know yourself and realize the significance of standing up for you. Life is too short and no one is worth losing your mind, body and spirit over.