I use a laptop, so just set the video camera running while I followed along with today's upper strength workout. I thought I was doing okay with regards with anything that requires a bending stance, such as rows, tricep kickbacks, etc. - but seems not. Whilst I feel I have a straight back, and make a conscious effort to keep it straight, my shoulders roll forwards. But I can't feel this, in my head, they're pulled back and everything's perfectly flat -.- Another thing I found which I hadn't noticed at all, is that I don't drop my left arm as far as my right when doing shoulder presses.
As I make sure I always squeeze whichever muscle is being worked on, and always stretch properly to cool down, I seem to have avoided any problems this could lead to with regard to back/shoulder issues. But it has certainly highlighted the problem and reinforced the importance of good form with me.
As I don't have a mirror, other than one above the bathroom sink (and a hand one), it's not that easy to check, but I'm going to start using my laptop camera to see my form as I'm lifting weights, and have the sound from the workout vids running in the background. It's not ideal, but it should work and once my body gets used to it, it should become instinctive.
I can't be the only one unable to use a mirror to workout to though, so I'm curious how others in this situation check their form?