Hi Rae,
I do remember what it was like to suddenly be thrust into a managerial position. And if it's your responsibility to make sure the clerk doesn't let the customers use the phone for free, and to even "weed out" the less-than-stellar employees, I hate to break it to ya, but you're a manager!
One starting point I could see is to try to find out what the employees thought of the previous manager. That can really help you figure out what route to take. THEY might have really disliked him, too -- that kind of disorganization can translate to late paychecks, or tyrranical policies, or all kinds of things that you can promise to rectify to help get them on board.
If they DID like him, you definitely have to tread more lightly. Do a lot of listening.
Also, do you have an employee handbook? Does it cover things like use of the phone? I worked at a company where employees would regularly get chastised for doing things that they didn't know were against the rules -- REALLY bad for morale. A handbook makes things nice and clear, and you can solicit some input to help employees feel more invested. Include not just rules but benefits, employee rights, etc.
Maybe find out more from your boss about this "weeding" business, too... is it because the staff have some issues that can be solved if they are more motivated and informed? Or does your boss expect that a certain percentage of the staff are going to go bye-bye, no matter what? And if so, why? Is it a money thing? If the staff increase profits to ____, can more of them stay? Can that be a motivator, rather than just up and getting rid of them? Is it a replacement thing, hiring new people rather than elminating positions? Etc.
Sorry for the barrage of questions, but all of this makes a difference in what advice I'd give, as ehBeth says. (And she has some great suggestions btw.)
Good luck!