Marry someone with a healthy heart. It will keep you from future heartache.
Go into business with people who exhibit integrity even when it seems easier and more profitable for them not to. Partners who value honesty are the best kind of people to sign contracts with.
Choose friends who are self-aware and not self-absorbed. They will be there when you need them and will be quick to admit fault when necessary.
You always end up paying in pain when you are unequally yoked in relationships, always. For the record, being evenly yoked has less to do with a belief system and more to do with being of one mind.