Just because you've been practising in a small rehearsal room and things sound pretty tight, it doesn't naturally follow that it'll all sound the same on the night. If you feel that all you have to do is set up and play just as you've been practising, there's a 99% chance of disaster. Many bands sound awful at their first gigs because they haven't balanced the on-stage sound.
You'll have grown accustomed to balancing to the drums when practising, but you'll need to be louder for your gigs. The answer is not to simply crank everything to 11. If you're struggling to hear yourself, don't get into a volume war with the other guitarist or bass player, it's most likely that the balance is wrong. Guitars will need 30 to 50 watts RMS to match the drums, and the bass will need 50 to 100 watts. Most reasonably experienced bands will meet these needs for small to medium sized venues. The vocalist is the one band member who will not be able to hear himself without monitors. By keeping within sensible levels, you can balance the volume of guitars and bass against drums - and keyboards if you have them. Each band member can move towards their back line kit to hear more clearly what they are playing, as well as checking out the other guys too.
To achieve a good balance, first set up the drums, then the back-line, followed by the monitors and PA; and make sure everything is functioning. Ideally the band should line up with the bassist to the drummer's left as it's the best eye-line for the drummer who needs to maintain good contact with the other half of the rhythm section. Ideally lead guitar is to the bass player's left, with rhythm on the drummer's right... again in line of sight and carefully aimed drumstick! The vocalist will be at the front, unfortunately that seems to be the way of things... stardom comes with a price! Start with the monitor volumes up but the PA right down, and send your sound engineer (or a willing volunteer with good ears) into the auditorium. Run through one of your best songs and check that everyone can hear what they need to. Check with the sound engineer as to how the instrument balance sounded. You'll need to make some compromises if one or two people are unhappy. Try moving them, or adjust the monitor positions. Check the angle that speaker cabs are facing in, you may need to move people away from something or perhaps move them closer.
Guitarists, don't forget that you have a tone control, and use it. Too much bass will create a muddiness, so leave the bassier bass to the man with four strings. You can control this at the guitar. Many guitar players simply set the tone knob to 'max' and forget about it. At this setting you will get the widest range of frequencies from your guitar, but try being more focused. Single coil pick-ups for example, can be very bright, sometimes more than you may like; to add some depth, simply roll off some top-end with the tone control.
The guitar also has a volume control and it's often used simply as an on-off switch - all or nothing. But it's a variable control, not a toggle switch, and it's meant to be versatile, so use it like this. With the volume control at max, set the amp to the highest gain/volume settings you intend to use, now turn down the guitar volume control for a cleaner sound for the quieter stuff you play. When you want more oomph, get a smooth change by turning your guitar volume control back up. While you are checking those maximum amp settings for gain and volume levels, check them rolled back a couple of degrees too; you'll often find a punchier and more cutting sound waiting for you. It's all too easy to tip over into a more squashed, thrashy, rock-out sound that is much more exciting on stage than it is for the audience.
This then is the sound check, a time for all to give their opinions. It's very rarely possible for everyone to get exactly what they want, so be professional and agree workable compromises. It's no good if people start turning up, or down later. Both the guy that wants to rock out at number 11 and the shy self-conscious player who backs off share one thing: they're both capable of ruining the entire mix.
Now it's time to agree the on-stage sound. Once this is set it doesn't get altered unless problems occur later, such as feedback issues or the crowd absorbing more, or less of the front of house sound than you'd anticipated. The whole band needs to agree not to change individual settings once you've decided on the balance. The sound engineer is the only person who should adjust volumes once the balance is set and needs to remember that the mix he can hear in his headphones will sound different to someone in the middle of a crowded venue. The engineer though, should never change the agreed on-stage sound balance (unless individuals have been cranking things up!). Communication between band members, and between band and engineer is essential. If anyone has a problem, use the time between songs to say so and sort it!
Finally, the PA. Everyone imagines this is the sound check - all that "one, two, one two" stuff is actually the last part. Remember that the PA needs to be set up so you can adjust the front-of-house sound separately from that going through the monitors. Run through a song, this time setting the initial volume for the vocals, they will sound loud without a crowd to soak them up and the sound will bounce back from the rear walls and floors. Adjust the back line if necessary. Play the noisiest songs for vocals and guitars, checking what happens when effects kick in or heavy distortion is added. Pay attention to the quietest bits too. This is a time for gentle tweaking and fine tuning, hopefully you'll have created the right balance in that first stage above! Play through a couple of numbers and make sure that everyone is as happy as possible. Once the crowd is in you'll need to fine tune some more but with the initial balance right, that's the easy part. Good luck!
