I began with something small: I forgave my teens for denting the car I gave them within the first week of having it.
Then I asked them to forgive me my shortcomings as a parent. This seemed easy, so I chose an old boyfriend who'd used a credit card of mine, racking up debt without my permission or knowledge and not paying it off.
Felt pretty good to energetically let that go. I then moved onto a more recent boyfriend who said some very nasty things in an argument, which ended our relationship. And then family.
Soon, people and situations I haven't thought of for years were coming to mind -- just showing up in front of me spontaneously asking for forgiveness and hugs. In the end, there was a wide circle of people around me in a group hug, and it was very powerful.