Think of something that's been bugging you - something that somebody did to wrong you, maybe, or just something that didn't strike you just right.
Think of this thing - and then try to forgive. Notice the word "try." Forgiveness is a difficult path, one that takes practice. For today, just accept the effort.
If you need a little reminder about how to forgive, here's one.
The beauty of forgiveness is in the trying. See what happens when you make the attempt.