No please, seriously; if the DJ playing before you is playing in the red, don’t just do the same mistake yourself, grab a long rubber hose and beat him unconscious, if there is a microphone, grab it, and have the joyful crowd hear him screaming for your mercy, of which of course you should give none in this case.
Being there such a majority of redliners among djs, and being people today somehow used to that squared/distorted sound, some of your crowd, especially the ones closer to the speakers might ask for more volume, but if you give those people what they want, you’ll do no good to your set. What you’ll do is screw up the things for anyone with some hearing left and/or a bit of taste.
Seriously, why would you take gain structure advice from someone who stands at a meter or less from a cranked up 20Kw soundsystem without a pair of earplugs? Maybe they’ll be pissed, but the rest of your crowd will be thankful, and, if wherever you’re playing there is a sound engineer or someone doing that job, you’ll probably earn his respect; they usually expect DJs to be apes with no understanding at all, they actually tell horror stories about Djs to each other; someone who can manage his/her levels will probably be a very welcome surprise.
On a sidenote, if you, like some DJs can’t tell the difference, and are actually happy with the mixer all cranked up, and ALL the red leds steadily on, please, look for work elsewhere; not saying you couldn’t tell if the levels are ok or not by just looking on the mixer in a decently set system, unless you’re also blind, but in an time when everyone or so is DJing, probably many shouldn’t, and if your ears can’t tell the difference, you’re probably one of those.
Luckily enough some guy from DjCity already managed to make a decent video explaining the basics of level management on most DJ mixers, so I don’t have to get into the technical details
I doubt I could add much to what Mojaxx said in that video