Squeeze the clutch lever with your fingertips, not the joints of your fingers - it helps make sure you get the lever all the way into the bar.
Adjust the gear lever so it's close to your toe/shoe/boot - it takes out the delay as you lift for the next gear.
Adjust almost all the free play out of the throttle cables, so that there's no lag - no slack throttle cable to take up as you re-open the throttle.
Accept that some days it'll snick, and some days it'll clunk...
To the above I'll also add the following copy and paste from an earlier thread:
Early on I found a few things about shifting 919s.
Let me rephrase, I found a few things, mostly related to rider, that resulted in duff shifts.
Slow lazy shifting results in more misses.
Crisp positive shifting gets better results.
A bit of lever preload helps huge, and some would say this is correct technique and not cheater technique.
Hard boots that provide no real lever feel at the toe can mess up things, especially if you have just transitioned from softer boots to hard boots.
Check linkage alignment, noting the fulcrum arms should have the centreline of their lengths parallel, one can too easily screw up the overall linkage geometry by poor adjustment and/or being off a spline or two by incorrect location of the splined fit.
It seems the harder the 919 tranny is worked, the better it shifts.
I found my poor technique most apparent on 5-6 shifts, for whatever reason I do not know.
Keep in mind all the co-ordination that's needed.
Clutch, throttle and shifter movements AND timing, that rely on two hands and one foot being in harmony.
Rough shifts mean problematic movements and/or timing are involved, assuming that there are no throttle cables and/or clutch cable mechanical issues.
Keep in mind that throttle controls revs and power level, so for example, the right RPM level in association with inadequate throttle opening when the clutch engages the power to the rear wheel results in engine braking.
Break down the elements and work on them until you are happy with the results.
Smooth hands and feet timed right and moved just so, does it all.