When you are measuring out your flour, sugar, etc with the measuring cups, is it better to   scoop and then shake the cup to get a leveled cup, or scoop and then use a knife to scrape off the excess.    I have been using the first method but will it make a difference?  
The real answer is that it depends on the measurement methodology used by the person who wrote the recipe. I have one book that actually calls for measuring by scooping with the measuring cup and scraping it with the side of the bag, which is how the average person tends to measure flour, and results in about 30% more flour by weight per cup.  King Arthur flour (and most other recipe sources) use the "sprinkle the flour into the measuring cup with a spoon and then level with a knife" which most closely simulates measuring sifted flour. This method will generally be appropriate when using professional recipes, unless the cookbook calls for another method. These recipes generally do not want compacted flour. If you are compacting your flour you are almost certain to be using too much.  Many instructional style cookbooks will lay out their measuring methodology at the beginning of the baking section (or the beginning of the book if it is a baking book). But since every methodology and every individual's use of that methodology comes out with a different weight per cup, working by weight really is your best bet. 