How do I prevent my fence gate from binding against the post?
First, determine why it is binding:


Is it because the wood has swollen due to wet weather, pests, etc.?
Is it because the posts surrounding the gate have shifted?
Has the ground shifted and moved the posts closer together?


My garden gate binds during wet weather.  Fortunately, we are much less likely to use the gate then.  The posts and gate are set to match perfectly when the wood is dry and that is when we most care about it working well.

If I were to do anything to make "wet closing" easier, I would bevel the striking surfaces so they wouldn't cause a dead stop, but move the posts apart so the gate can be closed with one hand.