Well I was once part of FC as one of their leaders so some points that I got from that time:

-Make rules and stick to them: We had rules for going up the ranks and about the time away from the game. Everyone that wanted to take a longer break should have told us and they would get a special rank to show that they are away but that its known. We needed the information because we did not want a FC that had big numbers but most of them to be "death" players, so we had rules about the amount of days someone could be gone without telling us about it. (They increased with the ranks) This kept our FC a bit small but still at least really active. We also said that certain points needed to be fulfilled for someone to increase their ranks. The lower ones where only about the time playing the game but the higher ones where only reachable if the person also helped greatly in the FC. Problem was at the end that sympathy started to overrule the rules and some of the leaders wanted to give some of the members higher ranks even if they did not fulfill the rule. This should normally be no problem if you are the solo leader but you should still try to do this fair, so that people will not feel bad.

-Tell the rules to the members. There is no sense in creating them if not everyone knows them.

The biggest problem we had where certain members that started to poison the environment with their behavior. Sadly we gave them too many chances and often we did not react strictly against them thus it created more anger. If there is a problem try to get the opinion of both sides and if its a smaller problem just talk to them about it. But one should not keep people in the FC if they are causing major problems or annoy other members too much.

Try to be there for your members but dont try to be the only one that does the work. Being the leader does imo not mean that you have to run every dungeon with every member or that you need to help with whatever problem you can. You need to enjoy your game too and if you notice that you are the only one that gives but does not get something from the rest you should probably have a talk with them. You will be the one that will hear about all the problems if people trust you enough (like telling you about some misbehaviors of others) and you should take care of it if its possible but you are really not the one that should to everything.