I did an online course on science of happiness from coursera.org, there I learned a very powerful tip, which helps me living my life more positively.
Write down three best things you did in your whole day.
Now write What happened
how you felt about it
and why you felt that way.
This exercise helped me in focusing on good things happened in whole day and 'why' of the question makes me think about essence of it and helps me be grateful for what I experienced during my day. This helps me live in present too.