One of the common problems people experience during gigs (and rehearsals) is not being able to hear each instrument, instruments may be too loud (or quiet) in the mix,  sometimes the vocals may not be clear enough.
Thinking about where you place each amplifier and monitor speaker can help you to overcome this problem. Instruments should not be competing with each other for volume, each instrument should sit comfortable in the mix to create a well-balanced sound for the whole band.

               Vocals:

Most people like the vocals to be a bit higher in the mix compared to the other instruments. Often a touch of reverb can help you achieve this ideal. It may be a good idea not to make the vocals to lound to start with, add reverb to make the vocals breath and go from there. Try various reverb settings. What you will find is that each song may require a different reverb setting. This may be good if the band does have a sound engineer who can monitor what is going on durnig the gig. Most of us will have to find a compromise in a reverb setting which works for most songs.  Make sure you know your equipment well enough to make small adjustments during the gig. Keep it simple for yourself with the adjustments you make, often you will not have much time to make adjustments, the better you know your equipment the less change you will make a mess of the sound.

              Guitar Amps and their Speakers:

Guitaramps do not project very well: Stand close to your amp and you may not be able to hear the details of your sound, even though your volume may be quite high. You can overcome this problem by angeling your speakercabinet a bit, if your are using a combo, just place the amp on something which will lift the amp a bit. Personally I like to angle my combo against something, the speaker will face up with the result you can hear the amp much better, and you can also hear the details in the sound. If possible, move a bit away from your amp, you will hear the sound much better, you may even like to turn down your volume a bit.

For all the different amps you are using with your band, try to set the amps up in a circle. Each person (hopefully) will be able to hear each individual amp. Try to match the volume of each amp, think about how someone plays. Some guitarplayers dig in hard in their strings, their volume may be a little less compared to the guitarists who play naturally quieter. Another piont is thickness of strings: thicker strings produce more volume compared to slinky strings. All of these deteils matter when you trying to get a good balance for each indidviual instrument.

             Monitors:

You can treat the monitors as little amps which contain the whole mix of the band. Most people in small bands will only use a handful of them, which means different bandmembers should share a monitor. Bassplayer and drummer may be able to share one monitor, while the guitarist and vocalist may be able to use the other one. Make sure each bandmember is happy with the monitor mix, do not start the gig (or rehearsal) before each bandmember is happy with the sound. Once everyone can hear what is going on your gig will be much better (and enjoyable).

            Size of the Room:

Work with the size of the room. A typical problem people encouter is: Turn amps up too loud, the sound cannot go anywhere because it does not match the room. The result is a deafening sound where no one can really hear anything at all.
Do not set the levels of your amp (and P.A) with your eyes, listen to the sound and work from there onwards.
When you play in a small room your amps can be quieter as when you play in a much larger room.
Listen to the acoustics of the room, any echo when you snap your fingers? Again, when you play in a echoy room you do not need to be too loud as the sound will reverbrate. Try to deaden some of the echo, but if not possible, try to work with the volume of the amps. Try to keep the volume as low as possible and let the echo of the room amplify the sound.

    
      Personal Taste:

A lot of what I mentioned before does not only depend on facts, there is also a lot of personal taste involved. When playing with others you need to check on how other people would like the sound to be: Some people like it to be loud, while others prefer a more quiter sound. Hopefully you can come to a happy balance where everyone can enjoy their own sound and the sound you all make together as a band.

Hope to catch you soon again,
Eddie