I agree with what everyone here says, communication!
DF and I have never actually had a "fight" per se, but we have had difficult talks. Both of us talk well through issues and we have had some very difficult talks, but, like Scarlett mentioned, we hang in there until the issue is resolved.
Another good thing is to learn to compromise (hey, this is good even when not in an LDR). For example, I am the much more emotional one during the periods of separation while DF deals with his feelings of missing me by closing up and not really talking about it. So, I learn not to constantly focus on my feelings of longing and such, and DF has learned to actually express his feelings of longing. So, we reach a middle ground.
Respect. Respect each other's time, opinions, decisions, thoughts, and lives in general. You play a huge part in each other's lives but you have to realize that you are not physically there on a daily basis, therefore, families and friends often seem to "get in the way" and take precedence.
Along with respect, you have to work on patience. I want my LDR to be over now, but, the reality is that I have to sell my condo, DF needs to find a bigger home, my dogs will need to finish out their 6 month wait which starts in May, and things always come up. It is frustrating but if you remain open with your partner and keep the communication going, you will pull through.