Step 1) Get rid of you mids with your vocals. In fact mids should only be used judiciously. They are the cheif reason many and I do mean many a mix has been ruined. Do it on the strip, you'll have to experiment because every board is different, but I typically turn the mids to -3db or even -6db. I punch up the bass and move the treble to just below the point where it hurts peoples ears. (Remember your vocal channels will be differnt than the others)
Step 2) Compress your vocals in a 2:1 ratio. It keeps the sound levels constant for the words. It's a professional thing to do.
Step 3) Right before your output to the amps, run a BBE sonic maximizer
http://www.musiciansfriend.com/product/BBE-362-Sonic-Maximizer?sku=180910
Step 4) Run your board's preamps such that they have a minimum of 60% gain (anything less filters out sound before it ever gets amplified) Trim the signals with the strip slider not the preamp. If your vocals are using phantom power or even another preamp you want to make sure you "open" up as much of the pre amplified signal as possible without distorting it. Anything less acts as a filter and you can never get back what isn't there.
Step 5) Use good mics for Pete's sake, nothing less than a SM58 or SM57.
Step 6) Contol all sound except the stage pressence (Which you need to police because you're dealing with musicians with amplifiers) at the board. They can have stage presence but don't let it muddy the overall sound.
Step 7) Bass guitar should be rich and low but not overpowering or mid range sounding.
Step 8) The drums are always always always a potential bomb waiting to explode. Some drummers know how to play with others, other drummers listened to too many drum solos and are literal deaf. Cymbal crashes are the most ear piercing thing (other than feedback) on a stage. If the drummer cannot or willnot drum quietly put him in a glass enclosure.
Step 9) All other rhythm instruments should be that rhythm. Don't put 5 acoustic guitars at the same volume as the vocals. Besides any more than one rhythm player creates potential problems because they don't strum in sequence. This adds tons of mids to the mix. Horn sections, clarinets and saxes, flutes etc. usually don't have this problem because they're all reading from a music sheet following their script which is to only play one note of a chord as oppossed to the entire chord like a piano or guitar player does.
Finally walk around once you dial the mix in. There will be hot spots (too loud) and dead spots (Can't hear the word) try as hard as you can to work those out by either compression, eq (get a good parametric eq) or even speaker placement. I've never understood why churches have to get these huge 1960 style electro voice speakers and place them up in the ceiling pointing down at an angle to just the middle sections of the church. Ever heard of BOSE? and Surround sound, small speaker concepts?