Edit: The following is intended for material that is already recorded. Use your hardware to check for live input clipping. If you clip on the way in your tracks are screwed. NEVER clip on the way in.
1) Use the Gain knobs at the top of the track strips to set your initial "start" volume for each track (before adding effects and whatnot). Leave your track Faders at 0db during this process. The Gain knobs are at the very start of the signal chain (so directly after the audio clips... basically it's like the "Input Trim" on an analog board).
2) Set each track's volume (using the gain knobs) to the "correct" level. That level may change depending on how many tracks are in the mix. They add up! The more tracks the louder things get. That's what Bapu was saying. -6db is actually kind of loud so as again noted by Bapu shoot for about -12db to maybe -8db on your TRACKS.
3) Create "Busses" for each set of instruments. So drums are sent to a drum bus, bass is sent to a bus (and many times you'll want multiple bass tracks being fed by a single performance but that's another story), rhythm guits to another bus, lead guits to another, lead and backing vox to their own, etc.
4) As those tracks hit those busses you'll want them hitting the busses so the busses register at about -6db each. If you set your Track Gain properly and you haven't sent too many tracks to a single bus it should be close. Use the Track Volume Faders to make any adjustments to acheive the -6db on each bus.
5) All busses go to the Master Bus (I usually set up a "Premaster" bus instead and then send that to the Master... I won't explain why here). All those -6db busses should more or less end up hitting the Master Bus at about -3db (this is the minimum amount of headroom you want to leave on your master bus for mixing.... the Mastering Engineering process makes up for the extra gain using limiters and other tools).
6) Use the various bus Volume Faders to make sure your Master Bus does not exceed -3db (again it's the mastering engineer's job to bring your mix up to braodcast volume which is -0.1db or as close to 0db without clipping as possible). Essentially your Master Bus should not be less than -6db and no more than -3db on a MIX.
Once you have set up your project in this way you can use the faders throughout the project (Track and Bus) to set levels how you like so all the sounds are cutting how you want.
At this point... as you add effects what you want to do is make sure NONE of the effects you add INCREASE or DECREASE volume on ANY of your tracks or busses (unless you intentionally want them to).
That is why pretty much all effects have "Output" level controls.
So what you do is add your effect, look at your track or bus meter (the one you added the effect to) then use the "Bypass" button on the effect to turn the effect off and on. You want the effect "On" volume to be the same as the effect "Off" volume. Use the effect's "Output Volume" control to make sure the peaks of the "On" and "Off" values are the same (by looking at the track or bus meters).
By doing that you do not ADD any extra volume in your carefully crafted signal chain while still getting the desired results from any effects you add to each track or bus... thus avoiding clipping from your effects.
That said... I am NOT a pro. This is just how I do my initial "Gain Staging". I go much crazier after that and some effects WANT to be driven harder (like they want more input signal to force the effect to work harder like a distortion effect or compressor).
There are also many systems for this type of thing. Again... this is just what I currently do, it seems to work but I am not a pro.
It should be a good start and keep you from clipping until you can learn more.
Cheers!