Forgiveness starts with you.
This means you are contrite for your own failings. You acknowledge in your own heart what wrong you did or what right you failed to do. You amend your life to do better.
This does not mean excusing or justifying your failings. This does not mean pretending you did nothing wrong or you harmed no one. This does not mean assuming your life is good enough as it is and needs no course correction.
So if you forgive yourself, then you must forgive your neighbor. For if you do not forgive your neighbor, then you presume yourself to stand above him.
Forgiving yourself, and forgiving your neighbor, are the first steps toward actually being in community. There is no civil society, let alone a faith community, without forgiveness of yourself and forgiveness of your neighbor.
Forgiveness is grace in action. Forgiveness is the first law in the Kingdom of Heaven. If you are religious, then forgive. If you “are not religious, but spiritual,” then forgive. If you are agnostic, then forgive. If you are an atheist, but tired finally of your own self-righteousness, then forgive. It does not matter where you start, if you forgive then you are making your first tentative step towards your true self, your neighbor, and God.