Gaining respect?

I started lessons in January, and have recently been moved up to a new lesson horse, one that requires a bit more effort and direction in his rider than my first horse. While I am very eager to work with him, I know that I have will have to put more effort into working him. He is a recent addition to the barn, coming from another lesson program where he was frequently given total beginners to pack around the ring. While I am by no means not a beginner myself, there are differences in my barn's approach and purpose compared to his old place.

There are things that he has been allowed to get away with in the past that now must be corrected (being pushy on the ground, refusing to stand to have his hooves cleaned, running his rider into the rail, etc..) he's not being mean per-say, but rather acting as he has previously been allowed. So my question is this, how do I make sure that I have his respect so that he knows that I am in charge, and what I say goes? I kind of tend to be a pushover naturally, and I need to make sure that I am not the weak link in putting this horse on the right path now that he is in his new home.

My question isn't really how to make him behave, but rather how do I behave, if that makes any sense. Although any pointers on that will be considered too. This is something that I have spoken with my instructor about too, but I do like to get input from many people, not just one opinion (which isn't to say that I am disagreeing with my instructor or some such, just that I like to hear from more than one person).