The old answer to this question used to be; "telling Him your plans for tomorrow" but the PDL has a series of better answers to the question. It is worth listing the things the Rick Warren says 'make God smile'...
1. God smiles when you love him supremely.
2. God smiles when we trust him completely.
3. God smiles when we obey him wholeheartedly.
4. God smiles when we praise and thank him continually.
5. God smiles when we use our abilities.
I could wish for a little more focus on No 5 but this is a good list of things that please God. It's not supposed to be comprehensive but it is a good start.
'Making God smile' is PDL's synonym for 'pleasing God' and that must always remind us of the Shorter Westminster Catechism's (SWC) answer to what is fundamentally the same question; what is the chief end of man? The answer is "Man's chief end is to glorify God and to enjoy him for ever". You will find some interesting commentaries on the SWC on The Shorter Westminster Catechism Project. I would particularly commend the comments of Thomas Watson which can be found on that page.
It is interesting to read this website and to compare it with the PDL's take on things. I know that the PDL is designed for a different kind of audience and that most people who would read the PDL will not be reading the SWC Project pages, but the differences are not just of style and substance but of focus. The SWC as befits its Reformed origins is 'God centred theology'. It is not just more 'dignified' than the PDL but somehow incorporates an entirely different viewpoint.
Giving God something to smile about is a somewhat different concept to 'Glorifying God and enjoying him forever'. Nevertheless theew are some good points in Day 09 of the PDL and the 5 points of Rick Warren's list may provide a helpful check list.