Really great baked goods start with properly measuring your flour. Flour gets compacted in the bag/canister, so if you just scoop it up with the measuring cup you'll be putting too much into your recipe. And that means dry hard muffins.
Run the blade of a knife over the top of the cup to scrape the excess flour back into it's storage container.
Tada!
Tips & Warnings
These steps are especially important for white flour, which compacts more than whole wheat flour.
If your recipe asks for sifted flour, the same approach applies - sift the flour (with a sifter or a sieve) over the measuring cup until it is overflowing then continue with Step 3.