4 Approaches:
Approach 1) Smooth and calm with lead in time.
1) No brakes
2) Let engine decrease speed
3) When you feel or know said speed is to low for gear, clutch in, drop a gear and smooth clutch out. Get's harder to be smooth as you go down the gears.
4) Tap rear brake to let others know ur slowing
Approach 2) Rev matching with less lead in time
1) 2 finger front brake
2) Forget the rear, as front is loaded already and engine braking will suffice.
3) Clutch in, jamb down 1 or 2 gears, depending on rate of deceleration. 2 is often good to reduce down gearing. Big throttle blip (jump up maybe 2 to 3k in revs - sometimes as much as 6k depending on engine type and speed differential (still braking with 2 fingers).
4) Feather out clutch smooth and fast. Bike lurtches into accelerated braking but not jumpy or choppy. Back tire may bobble, bounce or chirp a little. No problem, added braking as it catches up revs, and then slows you down.
Approach 3) Slipper clutch
1) get a bike with a slipper clutch
2) all the above steps are easier and smoother and almost 0 lurching unless you slam down 2 or 3 gears and dont bother rev matching.
Approach 4) Emergency braking
1) 2 finger, initial to progressive front brake.
2) 30% to 5% pressure on back brake as front end loads and rear lightens or bobbles
3) Clutch in, jamb down the gears to 1st. Hard front braking now.
4) Don't bother rev matching you dont have time or brain power.
5) When your down under 50kph jam into 1st and don't worry about the bobble....the rear is too light anyways to care...get ready for minor fish tailing. Partial feather or let go of the clutch in case of need to speed away or swerve to avoid hitting something else.
Advice...watch motogp slow-mo of riders bobbling the back wheel into turns....they are braking extremely hard before leaning, rev matching as they approach the turn and selecting the appropriate gear before, releasing the brake and feathering the clutch at the same time before leaning. Well...actually they often keep braking the front and rear well into the lean but decrease as they lean more.
Also watch their hands in reverse on boards, they will down gear and rev before the hard braking sometimes too!
So essentially.....they know before hand going into the turn it requires lets say 2nd gear, they are in 4th. Very quickly they downshift to 2nd, bike begins to brake, then quickly they add front brake. The bike will tip forward and their rear often comes up a couple centimeters. There is no point using back brake at this point because they want the tire to have traction when they get off the front brakes and reload the rear. The bike is also coming down to the appropriate rev band for the gear they selected before they started braking the front. Ideally, they want all wiggling, bobbling to be done while they are straight up, and by the time they begin to lean they want the rear to regain traction and the bike to be in the middle of the power band to be able to power out, sometimes a little under the peak power so when they apply constant throttle through the turn it isn't too jumpy. They may also opt at the point of leaning to gently apply back brake to slow rear tire rotation to scrub off more speed and to slide the rear to realign the bike for better exit vectors.
All of these steps slightly overlap one another. Meaning they may apply gentle front brake while rev matching at the begginning of deceleration. The hand can handle the more sensitive task of throttle blipping (90%) dedicated, while also 10% dedicated to the first stage (less sensitive at this point) of progressive front braking to load the front. When the front is beginning to load, and the work of engine braking has been done (i.e. the hand is now free to dedicate 100% to front braking, aaaaaaand the rear has scrubbed off effective speed - now no longer effective as the front is loaded and doing 90% of the bike's braking), the hand can be left to only deal with the front brake and also feel the bikes responses through the brake lever (sense vibrations, sponginess, chatter, etc.), and as the bike settles into the desired speed for the turn, the delicate task of trail braking into the turn receives 100% hand concentration. Again we have overlapping of front brake, decreasing as lean angle increases.
But first.....when you're just starting out, keep them seperate and simple. If you have time go down each gear, get used to it, get faster and better at it. If you don't have time, clutch in and bang down the gears, concentrating on front brake mostly. As you get better you will be able to dedicate mental and physical resources according to time, lean angle, knowledge of appropriate gear / speed, and so on. It becomes a harmonious symphony at the end, every body part instinctively knowing its roll through muscle memory!