Foot Position: the bass drum can be played heel-up, heel down, or anywhere in between. There also is the Heel-Toe method.

Take your pick. There are MANY "correct" playing methods. I like to watch other drummers and see how they operate their pedals, and I sometimes try different ways of playing after seeing someone else use a method I didn't think of before... Whatever works for you. Be open & flexible— I change my foot positioning depending on the song sometimes.

For heel-up, you are using the ball of your feet & the toes, somewhere around the middle of the pedal.
Find your 'sweet spot', where playing is most comfortable.

Shoes: I sometimes play barefoot. To me, playing in thick shoes is like playing with gloves on. Unfortunately, most clubs & rehearsal rooms are not usually clean, so for most projects I'll use thin sole sneakers. But for complex bass stuff, I play barefoot. That's just me.. To play the heel-toe method described below, you MUST be barefoot.

Is Your left foot weaker than your right? When you first move to double bass, you can't assume your
legs will be equal in strength. Your right leg (I'm assuming right-handing players, switch this for lefties)
has been playing bass for as long as you've been playing, while your left has not - so your left will be
much weaker.

I built up my left using Kenny Aronoff's Power Workout book. It really helped - plus it has made my right leg much better. I recommend it highly- not just for double bass drumming but for bass drum playing in general. You can apply it to single bass, but it roars with double bass. It works independent of legs & arms & builds up both legs. It is easy t start & you can work the exercises and a daily thing - I do the first workout with a few additions (I do the quads- 2 hand hits then left foot right foot then I do it again with a double foot on left then double foot right).

Just practice everyday. Start slowly, at a speed your weaker foot can do - it may seem too slow for your right leg, but you want to make sure your develop evenly & can keep steady with both legs, so start at the speed that you can keep at for longer than a minute. If you start at the speed your right leg can do, you will wear out your left too quickly.

To develop independence, don't just do alternating 16th. Try basic rudiments - also try playing basic
beats that would only require your right leg but use your left instead. Again SLOW BUT STEADY.

See PRACTICING

AND USE A METRONOME! GET ONE! It will really help make sure that you stay steady when you switch
from a single bass part to a double bas part. I tend to slow down when switching to double, so the
metronome is helping me learn to overcome that. Think of creative ways to use double bass - not just "budabudabudabuda".

See METRONOMES

Also, check out The Encyclopedia of Double Bass Drumming - I have it & it does have some good ideas. I think it is good to get that book too (Along with Kenny Aronoff's POWER WORKOUT)

Most Important: HAVE FUN!!!

Sitting Position: Make sure you are not sitting too high or too low. Your knee should be bent at about a 90 degree angle & you back should be straight. Now I find many drummers seem to sit too low, because they think they can get power by pushing at the bass drum. But in the long run I feel it slows you down. I like to sit a little high so that my feet 'dangle' a little on the pedal, so I can 'dance' on the pedals..

Balance: Trying to balance yourself on your stool without relying on your bass drum leg for support. If your leg is holding you up on the chair, it can't move as fast. It may be uncomfortable at first, but in the long run, you bass drum playing will be faster. Due to the fact that your leg is focusing on playing, not holding you up.

To Leave the Beater on the Head or Not: I think too much is made about not leaving the beater against the head after a hit. For some songs I PREFER the beater mashed into the head, for a real THUD sound. Less muffling needed, so the sound is still open. But no big boominess when not needed. You can also not mash it into the head when you prefer not to, for an un-choked sound. And again, since less muffling used, an even more open sound is achieved. I have also heard this, but as someone else commented, if you play heels up, you have trouble holding your leg up. Plus, most rock drummers muffle their bass drum—so lifting the beater off the head to let it resonate is pointless unless, you take out the muffling. If you play an un-muffled bass drum, or do not like the extra muffling caused by leaving the beater against the head, don't leave it against the head between beats.

And if fact, smashing the beater into the head seems to be the sound many drummers want. So it is really a matter of opinion. I usually play heels up & leave the beater against the head. And I usually am aware of it, & I prefer the muffled sound. That's just me....

BUT.... when using a double pedal it is very important to not leave the beater against the head - it messes up the sound of the opposing foot's beats! When playing with 2 bass drums, it doesn't matter, but with a double pedal, if you leave one beater against the head, hits by the other will be muffled.

Quick Doubles Using the Heel-Toe Method: The way I do heel-toe (not exactly as everyone does I think), you get doubles. First: your heel hits then the toe hits a 2nd beat right after, and yes, it is a sort of 'rocking' motion (so your foot is rocking - while you are rockin' ! ! er.. sorry...) anyway, you sort of 'snap' the beater down for a 2nd hit using your toes.

To do this method, your foot MUST be up high enough on the pedal so that your heel can push down the pedal - it's not easy like a normal hit, but when you get the rocking motion down you'll find it doesn't rely only on pressure - you also use the bounce of the pedal. You will possibly need to remove a toe stop of you have it, or move it away as far as possible.

To play this properly, I play barefoot. I find shoes reduce your feel with the pedals, much like gloves do with sticks. When people do play with gloves, they use thin or fingerless gloves.

The best I can do to actually explain the foot technique is this:

1) BAREFOOT - put your foot all the way to the top of the foot board - [get rid of any toe stop] your
     foot is higher up on the pedal than most people position their foot for heel up. It is more like
     heel down, with your foot totally covering the pedal.

2) push the beater against the head & hold it there (this is not a hit - this is the staring point for
     the demonstration of the technique)

3) Raise up your heel. The toes & ball of the foot should be holding down the beater still- that is
     sort of starting the previous beat - a regular heel up beat - that is actually not the first hit of
     this method. That is the position where you setup the next hit

4) quickly bring down the heel -releasing the toe pressure at the same time- heel should hit at
      the bottom of the pedal board with enough force to bounce the beater against the head - that's
      the 1st hit. This is done in one motion, you rock your foot backwards on the ball (lifting up your
      toes), and bring your heel down and 'snap' the pedal down (when you push your heel down
      to push the beater against the head - you make the 1st hit.)

5) immediately then push your toes back down against the foot board for the 2nd hit - while lifting
      the heel back up. ( Again 'rocking' your foot on the ball) After the 2nd hit - your foot should go back
      to the heel up position.

I hope that helps. Remember -Heel is 1st hit. Toes hit the 2nd.
(This is the method I use. I think there is an entirely different heel-toe method out there also)

Of course, there are various methods, this is just the method I learned (and I do use).

Setting Up the Pedals:I have both pedals pointing right at me (the main kick pedal points to my right leg, hi hat& slave kick pedal point to my left leg, so they are NOT parallel - because my legs are slightly spread apart & my feet also slightly angle out. They are positioned slightly wider than my shoulders.
The way to set them up - sit on your stool with no drum in front
of you - then slightly spread your legs out about shoulder width - let your feet fall and angle what is comfy. Then put your pedals under your feet so that they point the same as your feet. Setup the kit around that.