Forgiveness only truly comes when you see things differently, and then there is nothing to forgive. But until then, we keep working at it with all the techniques we know
Operationally, it helps to assume that what happened to you was similar to what you've done to others in a past lifetime (or perhaps this current lifetime) -- if not physically the same, then mentally and emotionally (in terms of anguish). Then forgive yourself for not knowing better at the time, ask for their forgiveness, ask for God's forgiveness, etc.
It also helps to remember Socrate's saying, "man only chooses the good; only that he does not know the real good from the illusory good." Innate to consciousness is the automatic selection of what seems like the best option at the time. Those options are usually obscured by layers and layers of faulty belief systems and illusions, but intrinsically, human consciousness is innocent. Everybody started out as a happy little baby girl or boy, and then their minds got programmed and brainwashed by all sorts of crap. We then look at people with compassion, that they are so trapped within the illusion that they think this outcome is what will bring them happiness.
By repeatedly looking at situations from a more benign point of view, the acceptance and forgiveness becomes automatic.
I highly recommend the workbook from A Course in Miracles on forgiveness.