Use a fine-mesh strainer
Tap the strainer gently over a bowl
Whisk the flour in a bowl
Shake the flour through a sieve
Use a fork to break up clumps
Use your fingers to crumble flour lumps
Pour flour from one bowl to another repeatedly
Add flour to a food processor and pulse briefly
Use a clean colander with small holes
Spoon flour into the measuring cup lightly and level it off