Hi hi,
Here's my two cents.
The first thing you do is set a budget, and stick to it. A little bit more here and there for slightly better mics and stands and cables and monitors and poweramps and before you know it, you've just priced yourself out of existence.
HOW BIG IS YOUR TRANSPORTATION? This matters. If you've got a van, great. You can go nuts. Get big mains, and lots of separate components. If, on the other hand, you have a Honda Civic, consider what is actually going to fit in the car.
You don't have to get premium components, to get adequate quality and function. Sure you can spend $300 for one Shure Beta 58 microphone, if that's what you really need. But, what if you need four mics? That's over a grand for just one element of the system.You can get a good dynamic mic for less, that will do the job. Check out deals on AKG and Samson, for example. Ask for a deal on a quantity purchase. Be careful about buying used mics. They can have the poo beaten out of them, and not show it. CHECK THEM OUT BEFORE BUYING.
You aren't going to need 100 foot mic cables often enough to spend the extra dough. 25 to 35 footers will do. Get serious speaker cable and plugs. Look for switchcraft plugs, and tough cable. Lamp cord is flimsy and can crack, short, and overheat(cause fires). This is a bad thing.
Look for mic stands with folding tripod legs and booms. You can spend up to a couple hundred for a mic stand but you don't have to. 45 bucks(in Canada)gets you a decent stand.
How many mixer channels do you REALLY need? If you're a duo, a compact six channel powered mixer should do. A quartet can get by with eight channels, but if you can afford a ten or twelve channel mixer, go for it. As far as powered versus unpowered mixers is concerned,using a separate poweramp will give you a more reliable power source, but it's nice to have your power and mixer all in one box. How useful are the eq controls on the board? Can you eq the monitors and mains separately? Is there phantom power for condensor mics?
AGAIN, IF YOU BUY A USED MIXER, HAVE A PRO SHOP CHECK ALL CHANNELS, FUSES, POTS, JACKS, AND PLUGS BEFORE PUTTING A SINGLE DOLLAR DOWN. ESPECIALLY, IF YOU'RE BUYING STUFF FROM A FRIEND.
Consider lighting of some kind. Get some gels colours (blue, amber, red)so you can be lit and not look like you drowned a month ago.
There are speakers/mains of virtually every size, shape, weight, and power-handling capacity. Consider your needs carefully. Do you need bass bins in addition to mid-high enclosures? How many monitors do you need? Can you get by with two? Four? Monitors come as passive, or with their own power source. Which ones are luxury, and which are must-have? Have you ever tried speakers with their own power source that eliminates the need for a power amp?
Now comes the fun part. Read. Read lots. Go to pro shops and ask lots of questions. See what they send out for rentals. Try out a rental system for a gig and see what it does for you. Ask friends what they use and why.
Above all, remember, this is an adventure in Techie land. Window shopping can be fun. So enjoy it. Really. Good luck.
Anyhoo, that's all I can think of for now.
Cheers.
Owl.