The discussion about the oven door and broiling (which has been bothering me for ages --every time I see Rachel Ray close her broiler I've wondered) has answered that question, but raised another. My mother always said when you're measuring flour for baking, not to smooth across the surface of the measuring cup with a knife, but to (hard to describe) tap across the surface with the edge of a knife, forcing the excess flour to the side and then out of the cup? My understanding was that this prevented packing the flour down, but if you watch Ina measure (or any one else for that matter), she's scraping across the surface with her finger, smoothing (even compacting it). What gives?
If you do a lot of baking, I think it's best to avoid the "how do I measure the dry stuff ' question and weigh it out. I've gotten much better results, esp with breads, since I started weighing everything...
Otherwise, I always read the intro to the book I'm baking from...All the good ones tell you how they arrived at the quantities in their recipes- Spoon in and level? Scoop and level with a knife? Etc...
Bunnyfood is spot on. Weigh if you can and if the recipe supplies weights. And see what any author has to say about how they've arrived at their measures. I do both, in that order, when I think a measurement is important. When I don't, it's the Ina method for me. The finger's right there; don't have to reach for a knife.
Tapping on the cup will cause the flour to compact. I tend to weigh when baking, but you can use the "scoop and sweep" method with the back of a knife, if you don't have a scale.
Bed Bath and Beyond sells a very nice Salter scale for about $30.00
I prefer to weigh the dry ingredients when I can. Trouble is, not too many recipes give weights - only volume (cups and spoons.)
When I'm using the cup method i aways stir up the flour with a large spoon to loosen it up a bit. As it sits it tends to compact and can give you a false measure. Then it's a quick scoop and swipe (usually with a finger and it's good to go.
I have my flour in a wide mouth container that lets me get the cup measure in and out easily without having to fight the paper bag it comes in.