Up to you.
The typical thing to do, would be to put your OS on the SSD, so it loads up faster, among other things.
Games or certain programs can also be put on the SSD, if you want them to be quicker.
A heavy program like PhotoShop would be good to put on the SSD; if you don't like the long wait.
Similarly a game put on the SSD will also load its levels faster oftentimes.
For mass storage, you then use the HDD. However it all depends on the size of your SSD.
Because if your SSD is only 120GB or less for instance, you won't have much room to play with.
Windows will bring that number down to 100GB and then if you install programs, it goes down further. Especially a game.
And with SSDs, you have to keep 10 to 20% of the remaining space free, to allow for it to maintain itself.
People usually buy a 1TB HDD, such as a WD Caviar Blue 1TB 7200RPM drive and couple it with a 120GB Samsung evo drive.
I would go for the classic confirguration mentioned above. So I wouldn't save pictures on the SSD, since space is precious on it
and there's no need for those pictures to load so quickly. But I would put Windows on it and perhaps one of my favourite games
or apps. I hope this answers your question.