You can either sift or use a wire whisk in your flour canister to lighten it and get out any lumps. Sifting or whisking incorporates air which helps make finer textured baked goods. When measuring flour use a flat knife to go across the top of your measuring cup to level it. Never tap or shake your measuring cup as this will compact the flour causing you to add more flour than needed.
If you are sifting the flour, add the salt, baking powder or baking soda to the flour so it incoporates it all evenly.