Start with the drums. Make a two-channel stereo mix from your recorded drum tracks, panning your overheads hard left and hard right, leaving your kick, snare and center tom centered. Have your hi-hat and floor tom slightly panned to give a natural stereo image of the kit as the audience would hear it.
Bring the bass guitar into the mix and play with the level until it nestles in with the drums and you get a cohesive-sounding rhythm section. You may have to perform a little minor tinkering with EQ to give clarity to the kick and the bass guitar, so that they have their own sonic space.
Work on the panning of the guitar tracks. If you have two electric guitar parts, for example, try panning one mostly left and the other mostly right. This will help give each of them more space to breathe and give you a nice stereo image.
If you also have an acoustic guitar track in the mix and you're having trouble making it heard without muddying the mix, reach for the EQ and roll off some of the lows from the acoustic track. Maybe even boost the highs a little. This will remove some of the low frequencies that may be competing with the bass guitar and drums, and give it a little more cut so that it can be heard without having to increase its volume. Why waste lower frequencies on an acoustic when they're largely unheard, and are more important to the bass and drums anyway?
Bring in the lead vocal and pan it to the center. It can take a lot of experimentation before you get the level of the vocal right. There's a fine line between having it audible and up-front enough, and having it sound too prominent. When this happens in a mix, it's almost like the vocal is perched atop the music rather than really sounding like it's a part of it.
Be careful when adding effects to the voice. Reverb, in particular is often overused in this respect. Too much can take away some of the presence and definition of the voice, and tends to move it away from the front of the mix. In contrast, a drier vocal sound tends to move the voice upfront. Experiment with this, but use a light touch. A good rule is to add reverb until you think it sounds good, and then roll it back a little.
Add the background vocals. Again, you'll need to experiment a little with your effects settings and panning to get the right amount of presence. Adding more reverb to vocal harmonies will make them more smooth and choral in nature, while leaving them drier will make them more pronounced. Experiment with the panning, too. Generally, moving them to around the 10 or 2 o'clock positions will give them enough separation from the lead vocal to be heard without being obtrusive.