Subsurf... and lots of subdivision. I actually hate subdividing because of all the unnecessary extra faces, but I do not know any other method that will give similar results.
I usually press k to open the cut menu, then use loop cut or the manual one. Sometimes triangulating works too, select a face and press ctrl t. Then subdivide that line that goes through or whatever you need to do. To remove uneeded triangles just select where you want to remove them and press alt j.