oh and if it's an amateur band tell them to turn the monitors down that's usually what causes most sound disasters with inexperienced groups.
get what you need (and only what you need) start with you Snare Hat and then play a song see if you can get away with that add what you must have from there, if you can't hear something don't turn it up turn everything else down makes the front of house engineers life better too which is another way of saying what the audience hears is better.
Also if not using a clip on make sure the mic technique is what works a good mic in the wrong place can sound worse than a mediocre mic placed well, get a good one and then play with where you are in relation to it.
using an SM 58 Vocal mic or Dog forbid a 57 could be 1/2 the problem
Vi should be mic'd with a suitable instrument Mic (condenser , medium pattern Cardiod) from overhead at the top of the instrument pointed away from the guitar amps and your monitor. a tall mic stand with a boom from the scroll about a foot above the instrument and angled away from the amps and monitor angle at 45 and 45 so it aims between the f-hole and bridge with the actual mic above the neck so it's out of the way of your Bow.
Stand on the Bass side of the stage let the guitarist have stage right helps with mic aiming and sound rejection if it's that type of band
You can always rent from a pro shop (companies that rent to touring groups) for a couple days to try stuff out (amps too)
hell call your local Orchestras sound guy (or Boston pops for that matter) and ask him what he uses for pops shows when they're not using a clip on (sound guys LOVE to talk shop)
try these.
http://www.akg.com/site/products/powerslave,id,223,pid,223,nodeid,2,_language,EN.html
http://www.audio-technica.com/cms/wired_mics/194ac5d60380d624/index.html
the AT is pretty heavy with it and it's shock mount needs a solid Mic stand so it doesn't droop it's a bit delicate but it's very flexible and can have 3 different pick up patterns, works really well if you want to do live and record solo. has an Omni directional setting so solo in a decent room it gets a lot of the room sound and can be used for area micing a wide array of instruments
the AKG was industry standard for exactly what you want for 30 years (until they discontinued it and got hate mail) this is a new version of that design
DPA also make a similar style of mic but again German for expensive.
http://www.dpamicrophones.com/en/products.aspx?c=Catalog&category=113
a good rule of thumb is the sound guy is going to show up with a cable with a XLR connector on it that runs back to his board, you need to provide him something to plug it into. that gives you control of "your sound" and makes his life better.
whether that's a mic above / on your acoustic instrument or for electric a mic that sits in front of your Amp or a DI (Direct input) box instead of an amp.
http://www.radialeng.com/re-jdi.htm
Don't assume the sound guy is going to have the right type of mic for your instrument and sound.
If you go electric I'd suggest googleing "pedal board" as an option (it's that thing at the guitar players feet) you may not need all the effects stuff but a volume pedal or Mute pedal a tuner pedal a DI box and a power supply for the pedals can make your life way easy ie: electrics don't make enough sound to be able to tune if there's any noise at all and they weigh a lot less than an Amp. keeps all your cables and stuff together as well much harder to lose things if you only have 2 cases to think about maybe get / make one that has a slot or 2 left open for effects you never know. also quite handy if your sharing the stage with other bands gets you in and out way faster only 2 things to move and plug in the XLR and 1 power cord.
(some amps have a direct out as well I'd recommend this if you go the with the Amp route you can mic the amp and / or take the DI signal)
make sure all the stuff you have is good and you like the sound it makes. (not going to crap out and makes a strong enough signal, any noise in the circuit is the enemy you never want to amplify noise)
if you go electric do yourself a favor and google "Unity gain" try and get your head wrapped around what it means the sound guy will Love you
lol apparently I'm bored I've written a novel on da internets and I know sounds like a lot for a hobby but there is a lot to be said for being able to set up plug in and sound check in 10 minutes especially for rehearsal you have way more fun if getting good sound is fast and easy