Just be rational and logical with your decisions; having similarity with someone personality-wise helps mostly because you will be more likely to keep in touch (not necessarily business) and keep discussions going. My collaborator and I were not "best buddies" before starting but we did have limited experience together in project based school work. Things like startupweekend might be a good testing ground [for a relationship]. I also found out being overly dismissive of your collaborator's approach on something is unnecessary; always be first to offer the other to prototype their idea out, if it sucks or is going nowhere, make your version. Be objective. The best way to find trust is to express it yourself. Be sure to take care of yourself, so that way if you do have to move on, you can do so painlessly.