Ask around. Ask your friends, ask your neighbors and get referrals. Nothing is more powerful than the testament of someone who has had a local plumber in their home and can speak to his/her capabilities.
When you have an outside faucet that is dripping it indicates that either you don't have an interior shut off valve or that the valve is failing. Every fall, when it gets cold enough to freeze, the homeowner should shut off and drain the water going to the outside water spigots.
Second, do you have the knowledge required to solve leaking pipes/faucets and clogged drain problems? You should be able to understand the parts of the faucet, pipes, and drain. Various types of faucets are sometimes designed to function very differently. You should know how to dissemble it replace the busted part and faucet replace put it back together again. If the problem is in the pipes, you should know which one you have to remove and replace.
Trustworthy. The best way to find a Trustworthy plumber is to ask a close friend, family, or a good neighbour for recommendations. They're the best people to ask because they've experienced the services first-hand and they will never lie to you about it. This works in the same way they won't let you hire someone who has worked for them and delivered bad service.
Now to prevent clogs from happening, you would need a drain cover in order to stop the clogging. However bear in mind that sometimes the best idea is to simply call your Local plumber and have them come out to take care of the clog. It is simply the more financially responsible as well as reasonable. Plumbers have equipment that the standard homeowner doesn't in order to clear the drains quickly and get them flowing again. Just remember that you have to be specific as your plumber is not a mind reader and cannot diagnose on vague information.
As precautionary measure, you have to tell all your tenants where their individual water shut off valve is located, as well as the entire building's so they can turn it off in case of emergency. And don't forget to make them accessible. It won't do any good if they know where it is but it's locked and they can't break in.
It is important to hire a professional for all of your plumbing needs. In order to protect your home and the investment you have made in it, you need to hire only the best contractor for any repairs.