Mirrors and Training I was always too busy working out I was doing crossfit, you don't need mirrors in ccrossfit. PTC doesn't even have a mirror in the bathroom....
Mirrors and Training train without a mirror, learn to use your body, film your lifts every once in a while. Majority of trainers tell every single person they see the EXACT same technique for every lift - feet go here, arms here, this depth etc etc... every body is different, we rely too heavily on what our eyes are telling us and forget to use our bodies for accurate feedback. Start paying attention to your muscles, what's firing? You may look really straight in the mirror doing some very nice looking squats but if all you can see is that it looks cool perhaps all your focusing on is that and not the fact that your glutes are sleeping and your hip flexors and quads are doing all the work.
Mirrors and Training When lifting u generally should be going by the feel in both bodybuilding and more so in powerlifting. least this gives u an idea if your actually doing the full ROM as each muscles fires up. best way to learn form is to film yourself on the phone camera at the gym from a 45 degree angle to get a accurate picture of where your going wrong. or have somebody knowledgable watching u. - Im pretty sure u cant look at yourself in the mirror when u flat bench on some heavy sets. Want your bench to come up? Pay attention via your muscles to each phase of the lift and what has failed or watch it on film. Everybody has a camera nowadays on their phones. I have guys deadlifting 250-300kg at PTC. All learnt to deadlift without a mirror. There warmup sets are the 9% the same as there maxes.