First, lets forgive ourselves for some past choices or behaviors that we might be regretting. We cannot undo the past; we can only change the future by making enlightened choices and behaving differently.
One very wise person shared with me that if we are not embarrassed by our past, we haven't grown.
Then lets forgive those that we might be holding a grudge or have less than positive feelings toward. Holding a grudge can be a colossal waste of one's emotional energy.
This can be a though one, but I have come to believe that people do the best they can at the time under the circumstances: parents, children, co-workers. If they had the ability to handle it differently (more respectively, truthful, considerable) then they would have.
The acceptance of this philosophy of human behavior makes the forgiving much easier and can change our perspective of those people so future interactions, if any, can be smoother.
Often time, people will be resistant to forgiving a person because they do not want to give that person the satisfaction or benefit of the forgiveness. I think this is a misguided concept, forgiveness is for the forgiver. One doesn't even have to speak to let the other person know of the forgiveness -- just forgive them. They did the best they could at the time under the circumstances. That is all anyone does.
Then try to learn to look at those people as teachers. What did I or can I learn from this experience or interaction? If you can shift your perspective, you can shift your reality.
If you can wrap your arms around this concept, grudges will melt away, tension will ease, and you can focus your emotional energy on positive endeavors.