#1 Start small.
Don’t expect that the level of trust that you once had will be rebuilt instantly. It takes time so start small and don’t expect too much from each other right away.
If they were the ones who broke the trust, you need to forgive them. Even if you’re still angry or hurt, you need to work towards forgiving them if you ever hope to rebuild the trust. You’ll never be able to move forward if you’re holding onto the issue.