John Gottman and "The Magic Ratio" -- 5 to 1 meaning healthy relationships have 5 times more positive communication than negative. Make sure positive comments outnumber negative ones by a healthy ratio. Gottman's is an easy guideline to remember.
People with CPTSD are often challenged when trying to maintain boundaries. Usually they grew up where boundaries were not respected. The ability to maintain boundaries can help facilitate healthy relationship and safety.
A great article to help partners understand the difference between complaining. Constant criticism can create a great amount of tension in a relationship and often stems from ineffective communication styles.