You can't change what you're not aware of, so here we are - awareness is the key to improving your music practice and getting better results. As far from music and as unspecific this approach may seem, it definitely deserves any musician's attention. So read on...
Being aware of what is happening usually precedes the 'rush to judgement'. Awareness is a non-judgemental state which allows one to see everything clearly, exactly as it is – without the filters of one's ideas of good and bad, or right and wrong. In the Inner Game, it is the first of three fundamental skills, which also emphasizes its particularly important function.
When one is simply aware of the extent to which the results of one's actions match the intentions, one learns in a natural way. This approach allows one to accept the reality and inhibits the urge to fight it or change it immediately. The feedback based on what one can see, hear, feel and what one knows works or not, helps an individual “to choose the most natural direction in which to change.” (1) This happens because one's body is given clues about what to adjust at a level below one's conscious awareness, and without any interference – either mental or physical.
(1) Green, B., with Gallwey, W. T., The Inner Game of music, Pan Books, 1987, 57
[From Music Practice Decoded. The Psychology of Getting Brilliant in Music, Part 5: Awareness and attention - the key to successful change]
If you don't really know how this works in practice, here are 3 simple ideas you can try out in order to improve your awareness and start using it more than thus far.
1) Before you start your practice, spend a few minutes just breathing (you can also meditate). You are more aware when your brain slows down and becomes more connected to whatever really is - your posture, what it feels like when you breathe, what you want to focus on... When your head is crowded with thoughts, ideas and worries, it's impossible to be in the present moment. Apart from that, a huge part of music practice is about muscle memory, so it's really helpful when you know what you want to reinforce, repeat and remember as opposed to what doesn't work and leads you to poor performance, tension, or maybe even pain. Be aware and decided, don't let things just happen randomly when you practice.
2) When you practice, use from time to time a mirror to observe yourself while playing/singing, or - even better - film yourself for a few minutes. A camera in your laptop or smartphone would be good enough. A video can show you when you get tense, make faces you don't really feel like making on the stage, or basically show your (imaginary) audience, which fragments are really difficult. When you have such clear feedback, it's easier to focus on what needs to be improved.
3) Take a few Alexander Technique or yoga lessons, or try out any other technique that can help you to be more aware of your body and breathing. You don't need to be sporty or sweat every day for an hour to learn how your body works. You want to play or sing in a natural way, so if you start with what you already have, the process is going to be way simpler!