I treat mine mostly like any other hard drive. Everything that you use frequently and want to run faster should be there. You would need another hard drive to put things elsewhere. I do have a second hd where I install games and other junk. A third hd for downloaded files. MAYBE if I catch a downloaded bug it might stay there and not bother the rest quickly; probably wishful thinking on my part.
I install OS, and software on SSD. Reads don't affect it, it is writes, but even still, you are going to upgrade SSD before it dies. Use SSD for things where speed matters, like launching software and booting OS and HDD for things like music/video and other junk. Oh, move download folders/documents and other things that get written to frequently off the SSD.
Put everything on it except your swapfile. SSD's don't like lots of tiny writes and reads. You can find cheap 8gb or 16 gb ssds on ebay to put the swap file on. Overprovision them, make sure they're aligned (win 7 and 8 do this automatically) and you're good to go..
