For me, it really depends on how fussy the block is. If it's just something simple like 4 patches I usually don't press at all until the whole quilt top is done - finger-pressing does well enough for assembling simple blocks.
Usually I just press with a dry iron and that does well enough. Complex blocks that have lots of intersecting seams, I will bust out the steam and the clapper. If I'm going to use starch or Best Press, I will have done that before I cut (or before I sew, if I've forgotten to do it before cutting). I don't usually starch completed blocks.