Always sit with your back straight when playing the drums (or any musical instrument for that matter). Yes, what your mom told you about slouching is true. If you slouch when you play, you are begging for back problems later in life. It just stands to reason. The stronger your foundation, the stronger your sound will be. So sit straight. You will look better, sound better, and feel better. It's a good idea all the way around.
Dancers practice in front of a mirror so that they can watch every movement they make and make corrections. The same applies here — you will be able to see if you are holding the sticks correctly, if you are making all the stick heights the same, etc. It's just a really good way to practice.
When learning beginning strokes on the snare drum, practice at an extremely slow pace in order to make all the strokes sound exactly the same from hand to hand. In order for all the strokes to sound the same, they must look the same, so the sticks are held in a V-shape, 7 to 10 inches above the center of the drum. The sticks should always come down from this position and rebound in one single movement back to this position.
When practicing rudiments (or anything you may do on drumset) always practice with your metronome. Think of the metronome as your band. Then when you take the metronome away and you are out playing on your real gig or jamming in the garage with your guitar buddies, they will be amazed at what a steady beat you can keep. The ability to keep a steady beat will keep you in demand as a player.
The Karate Kid (first movie) should be mandatory viewing for every beginning drum student. What a sublime lesson in learning to master anything. How do you get that hard part of that song that you seem to stumble over every time you get to it? You slowly practice that one part over and over and over again. And then, over and over some more. And some more the next day. Then the day after that and the day after that. Before you know it you are playing that song and breezing through that "hard" part with the greatest of ease!
Lessons provide instruction, encouragement and constructive feedback. This will help you progress quickly and develop good form that will serve you in the long run. Videos are good for general knowledge and can be fun tools to use as a supplement to your lessons. Remember, the instructor on the video cannot watch you play and help correct any bad habits you may be forming. Please take lessons with an experienced drummer and teacher. If you're in the Houston, TX area and would like to take lessons, please contact me- firstname.lastname@example.org