When training on my own, self-correction is very important, so there are a few things I do to determine whether or not my technique is as it should be.
The first is by feel. Sometimes I close my eyes and execute a move – immediately I can feel if my stance is too wide, narrow or just plain wrong, if my punch is at the correct height, or if my shoulders are relaxed or not etc. I've learned to trust this approach, because my body will always tell me the truth, whether I want to hear it or not.
The second is by looking in the mirror. That (wo)man in the mirror is never perfect darn it! She's always got something that needs fixing and it is my job to change her ways – I often become frustrated though at how easily she becomes frustrated, but I do try to remain patient with her. I make sure to take the time and really look closely at every detail - of course this slows the training down, but there are days when you just have to take a step back and work from the ground up, making sure everything from toes to posture is correct, in other words: take a look at yourself and make that change.
However, when all else fails, sometimes it is better to let Sensei step in. He's much more kind to her than I am.
And one final note for today: Happy Birthday.