To begin with our inner critic can be so overwhelming and that is all that we think of. But as we take the focus off that and do more things to take care of ourselves, as someone said, it goes quiet.
But it is always there nagging away and can be the things that we think and say to ourselves or even to others as well as in our sleep that can be the underlying critic.
The key is being able to look at that critic and learn to question it with things like:
What evidence is there that this is true? Does this happen in all situations or just occasionally? Is everyone this way? Does everyone that I know think ill of me? Would I say this to someone else in this same situation? Does this make me feel better and/or help me to achieve my goals?
Once you can establish if it is valid or not - you can then be more reasonable and positive about it.
The key is to replace it with something positive.
Critic: 'No one likes me anymore'
Validation: 'Many people don't like me, but there are many people who do like me and value me.'
Replacement: 'Not everyone is cruel, there are many kind ones out there too.'
I could go through other examples but I think you can gather the benefits of this skill.