The Art of Being Positive:

Keep looking up; remember there is only mud under your feet.

An optimist sees an opportunity in every calamity; 

A pessimist sees a calamity in every opportunity.

--Sir Winston Churchill

Ella Wheeler Wilcox gives us some wise counsel in her poem "Optimism":

Talk happiness.  

The world is sad enough Without your woes. 

No path is wholly rough;

Look for the places that are smooth and clear,

And speak of those, to rest the weary ear

Of those so hurt by continuous strain

Of human discontent and grief and pain.

Talk faith.  

The world is better off without

Your uttered ignorance and morbid doubt.

If you have faith in God, or Man, or self,

Say so. If not, push back upon the shelf

Of silence all your thoughts, till faith shall come;

No one will grieve because your lips are dumb.

Talk health.  

The dreary, never-changing tale

Of mortal maladies is worn and stale.

You cannot charm, or interest, or please

By harping on that minor chord--disease.

Say you are well, or all is well with you,

And God shall hear your words and make them true.