The basic work of mindfulness is to put a filter on your mind. You watch your thoughts and when you notice yourself thinking bad things about yourself, or others, you just say “judging” and the thought goes away. If you get frustrated with yourself because you find yourself judging a lot, then just say, “judging” and the thought will go away.
Watching individual thoughts is a fine filter. Watching your moods is another level of filtering. If you notice that you are in a bad mood, you know to be extra alert to watch for those negative thoughts. You can see if your thoughts cause your moods or your moods cause your thoughts. When you notice that you are in a bad mood and you see a negative thought, just say “judging”, and the thought will go away. Maybe the mood will go away too.