First, lets tackle backing it in, then we'll look at drifting....
1. bike setup - just keep it the same as normal and what you're used to - changing settings will make the bike feel different and therefore how will you know how it feels to start sliding? Making changes adds to the confusion and as with engine development - do one thing at a time!
2. Understand the process first and what we're trying to achieve:
a) It's not just to look good - it's about getting the bike into a better position to get the rider through and out of the corner as fast as possible.
Backing it in is therefore about getting the bike pointing further in the direction you want the bike to go so that you're then able to get on the throttle harder and earlier, and spending less time leaning too far over to get on the throttle properly - if you know what I mean.
This should also answer the question as to when to back it in - only when it's the best thing to do - in other corners, knee down superbike style may be the best and fastest way round - use your judgment - it depends on the corner.
b) It's about preparing for getting out of the corner fastest therefore it is about being set up for getting straight on the gas when you hit the apex or point at which you want to fire out of the corner (whichever is most appropriate).
This should answer your question about what and how many gears you need to knock it down as you back it in - if it is a first gear corner, you knock the gearbox down to first, if it is second, you knock it down to second. And that means even if you're in sixth gear and you approach the corner. It is not as scary as it sounds and we'll build up to that....
c) You never lock the rear wheel - but you do break traction (obviously).
To do this with good control and stability you will use a mixture of the gearbox, clutch and rear brake. Notice that I don't mention the front - that is because as per normal you'll most probably be braking as hard as you can with the front brake - so nothing has changed there then
3. Breaking the traction - which is what we need to do first. This is done with the gearbox - dropping down the required number of gears and the literally dumping the clutch - after you have started leaning the bike over. As the traction breaks, the rear wheel will slight out sideways.
The best way to practice this is in a car park or somewhere similar where you can simply go straight back and forwards, making sharp turns at each end round a cone or something. For the purpose of practice select the place to do it so that you can get up to third gear, going down to first. As you ride towards your corner, make sure you're sat well forwards on your seat and if possible your body position should at the very least be held completely in line with the bike as you leaning but ideally should always be leaning slightly further to the inside even with your inside bum cheek slightly off the seat - do not whatever you do try ti sit on the bike like they do in MX (you'll find out why later). The following steps happen in rather quick succession:
1. You start braking for the corner with your front brake to transfer weight to the front (that's also one of the reasons you need to sit forwards on the bike).
2. As you begin to brake you will obviously pull in the clutch and now drop down two gears.
2. Begin leaning yourself and bike into the corner - just do this gradually for now
3. Dump the clutch - just let it out suddenly.
You will find out if you have the right amount of lean angle into the corner when the rear begins to break away sideways. To begin with an inch feels like a mile, that is why you gradually increase lean angle. When you get used to it you'll happily do it whatever lean angle you're at.
What you will find when practicing this is that the rear will slide out and very quickly come back into line before the apex - we resolve this with the rear brake.Get used to this breaking away feeling first using only the gearbox and clutch.
The reason the rear brake is used is to maintain a constant but slow rotation of the rear wheel. What you'll have noticed is that if you just use your clutch, the engine revs quickly increase as friction between tyre and tarmac pull the wheel round quicker - that is why you experience the rear coming into line quite quickly. The rear brake is used to add more friction so that engine revs don't rise and the rear wheel maintains its slower rotation. That is all the rear brake is used for! So it is done gently!
So lets add this to the above process:
1. Set yourself up on bike, begin breaking with the front and add a little rear brake
2. Drop down through the gears
3. Lean in
4. Dump clutch
You will notice whether you're getting the rear brake pressure right by how well the bike maintains its slide to the apex. When you practice this you will also know why we only add the rear brake after you've learnt how to initiate the slide.
What you may also notice when doing these exercises is that the rear wheel may begin hop - this is rectified by using the clutch and just pulling it in very slightly.
As you practice the above you will also notice that the degree to which you're sliding varies and that you can vary it yourself, depending on the corner - this is done using the clutch and very slight adjustments on the clutch lever as your backing it in to the corner - this bit is the bit that really requires the practice and skill and marks the difference between those who can slide and those who can sliiiiiiide.!
You may notice that none of this means you have to be absolutely on it or riding aggressively to slide - it's actually a very gentle technique when you get to know it.
That should be enough to get you started........
As for the drifting bit, I think the first thing you need to do is get used to doing it on your sm bike with slicks on loose gravel or something similar and as above doing this between a couple of cones so that you're going round a couple of really tight turns getting on the power so that the bike spins round the corner, if necessary with your inside foot on the ground to give support. The really important thing to remember is that as the bike begins to slide you lean your body to the inside of the bike and also ever so slightly bringing the bike more upright (look at dirttrackers). Once you've got comfortable with this on the loose stuff, then get onto tarmac and begin with learning how to do donuts, first with the bike really leaning over stood still and with one leg on the ground. Then get used to breaking traction and pivoting yourself on you leg round in circles as the rear burns away (it is also quite good to start this on loose stuff to get used to the feel).
One point about drifting and that is really difficult for some riders to get their heads around is that you do not, whatever you do, chop the throttle! If a drift starts going too far you regulate it by holding the throttle and/or by pushing the bike more upright.
As an interesting point Valentino Rossi practices his drifting in a quarry with a bike with an MX front tyre and road rear tyre!
This should also be enough to get you started.