I started out making clothes and other items where the seams were pressed open. Then my first quilt instructor said "press to the dark", which I generally do, however, when you are piecing a block with many pieces, it's better to press your seams open to reduce bulk. You can finger press or use the wooden iron - a favorite of Eleanor Burns, and then if you need to use the iron go ahead, but I've found that the wooden iron works pretty well. The "rules" do constantly change, but use what works best for you and you'll have good results.