Decide to not hold on to your pessimism. Choose today to be optimistic. Choose to look at the beauty around you and to see life and people through loving eyes.
That is all it takes.
Surround yourself with optimistic happy people. Do not engage in conversation when people are complaining about their children or husbands. If a friend comes to complain about her kids I try to turn around and point out to them how that characteristic could be good or some other great thing about their children. Or I change the subject.
Look at what you have, not what you do not have. If all you focus is in negative things that is all you will see. If you always look for the positive slowly you will, more and more, see the positive and the beauty around you and that will become who you are.