The Serenity Prayer is commonly known as follows:
God grant me the serenity
to accept the things I cannot change;
courage to change the things I can;
and wisdom to know the difference.
Few lay-people, though, know that it is part of a longer (and very beautiful) prayer, by Reinhold Niebuhr. This longer prayer is easily available on the web, so you might be interested to find it, if you don’t already know it.