You are not alone when you say it is hardest to forgive yourself. Most of us are harder on ourselves than on others. So, welcome to a large and not-so-exclusive club. The pathway to forgiving oneself is actually not that different from forgiving other people. That pathway, of forgiving others, is discussed in detail in the book, Forgiveness Is a Choice (available for purchase from this website). I recommend that book because the forgiveness pathway described there has the most scientific support of any forgiveness model out there.
OK, now to self-forgiveness. When you forgive yourself, the complication is that you are both an offended person and an offender. At the very least, you have offended yourself, you have broken your own standard in what you did or said. And, I might add, we rarely offend ourselves in isolation. So, a first step may be to go to those whom you have offended and say you are sorry and ask for forgiveness. Please realize that those whom you approach may or may not be ready to give the gift of forgiveness. Thus, please be patient and understanding. A second step then is to offer to yourself in forgiveness what you offer to others when you forgive them—compassion, gentleness, understanding, and love. Yes, even love. Give yourself permission, as an imperfect person, to love yourself despite what you did to offend yourself. You are larger than your actions and words. You are more important than only your unjust words and actions, as is every person in the world. Allow this perspective toward yourself to gently wash over you until you believe it. This is the essence of self-forgiveness.
Learn more at Self-Forgiveness.