Developing a feeding routine is a good way to help establish you as the herd leader. One of the times when your horse is the most aggressive is at feeding time so it one of the best times to determine leadership.
Basically a feeding routine is anything that you have your horse do that they must acknowledge you as the leader before they get fed.
Sometimes it's helpful to have an example of a feeding routine. Here are a couple of examples that you might find useful.
Here is a routine I started while in Florida a few years ago. It was not solid at the time of the video but it was coming along. This video was taken from my coaching program and I am explaining to the members what is happening.
Note: As I stated before, feeding time brings out the dominate nature of your horse. Be aware that they might challenge you. Stay safe and you may need to stay on the opposite side of the fence until they begin to acknowledge you as the leader.
Here is what a good friend and fellow instructor Ron Pyne does with his horses. This one is amazing but shows you what is possible if you put the time in.
Both videos show something that has taken a good amount of time to develop. You should start with something simple like having your horse stand back (maybe with their rump on the fence or wall) before you give them their food.
The best way to begin is to start simple and build to harder and more elaborate routines. Make sure that it becomes a routine before you start to add more elements. Take your time and sometimes it's best to start with one horse and make sure each horse knows the routine individually and then add them together when the time is right.
I hope this gives you some ideas to get you started.