The proper ways to do curtains is as follows:
Brushing the floor: Structured Style
Positives: Gives off a clean cut and tailored room. No fuss!
Negatives: If you have problem floors then the crisp cut of the curtain will call attention to your uneven floor.
Breaking the Floor: Relaxed and Glam!
Positives: Gives your room a softer look. My favorite part about it is that it’s forgiving of imperfect measuring.
Negatives: Because your curtain panel will be 1 or 2” on the floor some may be nervous that it will get dirty easier.
Pooling at the Floor: Lush! ( This is my favorite)
Positives: Gives off a romantic feel with 2 plus inches on the floor.
Negatives: Same as with breaking the floor. Plus due to all of the extra floor you will not notice any sort of moulding/trim on the floor.
Here is a great sketch of the looks featured above by I dream of drapery:
Floor Length = Brushing the Floor
Trouser Length= Breaking the Floor
Pooling at the Floor = Puddle Length