What might be more fruitful: to forgive someone else or to forgive myself first?

Because we tend to be harder on ourselves than we are on other people, I usually recommend first trying to forgive other people.  Become familiar with this process: seeing the inherent worth in the other, softening your heart toward the other, bearing the pain so you do not hurt the other.  Once you have a sense of these aspects of forgiveness, then apply the same themes to yourself: know you have inherent worth, not because of what you did but in spite of this.  Soften your heart toward yourself, again not because of what you did, but in spite of this.  Commit to not harming yourself.  One aspect of self-forgiveness that differs from forgiving others is this:  In your self-forgiving, examine whether you might have hurt other people by your actions (that require self-forgiveness).  Go to those whom you have offended and ask for forgiveness.

Learn more at Self-Forgiveness and Learning to Forgive Others.