I admit, I need lots of praise ("gold stars") to maintain enthusiasm for jobs.  But I'm probably not that great at giving it.  The Happiness Project advises:

• be specific – don't just say "Well done!  That's great!"
• acknowledge who did it – don't just say "that was good"
• be as effusive as the act deserves – if it was a huge deal, put some effort into it.  Several times!
• beware the negativity bias.  Saying 1 negative thing at the end of 5 positive things tends to cancel out all the positive stuff.
• praise the everyday.  Do you remember to thank people for their daily, routine contributions?