Let's start with our mistakes and disappoinments, select and forget about all them. We have to clean our mind, no bitterness, no regrets. Just keep the things we've learned from the moments we've been through, because at least the difficulties make us stronger.
Now, let's think about the great moments, remember of someone you met after a long time, a view of the sunset, a trip, a party, a smile that you caused, a victory of your team, a hug, a kiss, something that makes you happy. Memorize these moments because they make the life worth living.