First of all  you will need a good solid drum stool.

I sit quite low, about 18'' from the floor. A lot of drummers I see also sit quite low.

I make sure my lower and upper back is straight without being tense. Shoulders are back but comfortable, elbows free to move against my sides. 

Make sure you are not hunched over or crouched. If you are experiencing neck or lower back pain, review your posture

Once seated I balance myself with my feet on my pedals, heels slightly off the foot plates. Knees are spread with the snare positioned at a comfortable height.

 Try and reach everything from your drum stool without having to lean forward, but at the same time you don't want to be constricted and boxed in. Try and find a happy medium.

My high\hat foot is positioned slightly back from bass drum foot and I am angled slightly toward my high\hats, 
for all the above.

IMPORTANT Its a good idea not to have your snare drum too low. Try to get used to having it at a height where you can execute a rimshot hitting the rim and centre of your drum at the same time, done by experienced drummers,

We will be covering rimshots thoroughly in a near future lesson. Although at this stage you are only hitting in the centre of your snare drum, its important that you get used to your snare being at a height that you can execute a rim shot. I like to have my snare drum tilted slightly toward me.

I like my toms at a level and height that is comfortable. The angle  comes down to the individual, depending on your height etc,

The angle and height of your cymbals and high\hats also differs from person to person. See PLAYING CYMBALS AND HIGH\HATS.