[long response, just some basics to the question..
otherwise just scroll on bye
our brains motor cortex is very sensitive to hands,
and the 30 or so forearm muscles moving fingers
plus muscles in palms moving thumbs and pinkies..
hand habits picked up or developed seem stronger
yet we can take advantage of our human brain
and hands and teach/train them to skills
according to our needs,, including riding..
riding instructors [incl as in jkv's 10 hints above]
often advise riders to position their fingers
1, 2 or more of them out over the levers..
one basic reality for this being that smash events
are measured in microseconds, thus in emergency
braking fingers resting over levers have already
begun the braking response,, rather than needing
to unclench a grip then start extending them
up towards and over the lever before starting
[bang!! too late] their braking response..
also fingers over levers are constantly sending data
back and forth to brains motor cortex - brain training..
especially when one or two fingers are used
for ongoing minor speed variations..
ongoing finger/braking training..
all sorts of riders up to and including motogp
use fingers over levers as a basic riding skill..
ie, its not some unusual or difficult thing..
the hard thing is to ride while continually gripping
the bars,, which is hand abuse, and not the option
for most efficient braking responses..
[point on motogp riders being their ongoing
high stress environment with essential need for
excellence in braking and control skills]
thumb has its own muscle in palm, as does pinkie,
which means they can move independently
including as part of throttle controls..
thumb includes its webbing to index finger
which makes good contact with the throttle
providing necessary friction together with pinkie
for more than enough effect on turning throttle..
hands should be relaxed when riding generally..
start by thinking 'relax hands'.. i like to stretch fingers
and hands just before taking off,, rubbing them together
and as if washing them with each other [that action]
making fists, stretching fingers outward [etc]
then placing hands on bars,, not, gripping..
moving levers in and out with fingers..
[or whatever suits you]
to begin with, from clenching bars, start by resting
index finger on levers [acts as a 'sighter', anyway]
then ride as usual, mindful of relaxed hands..
think of the action of a rolling pin rolling dough..
then add thumb and webbing behind/under
bar, together with pinkie flexed on bar..
proceed as usual, mindful of relaxed position..
when comfortable, also extend middle finger out,
resting on lever.. practice pulling lever a few times..
then ride as usual.. best option being a practice site
as for your usual riding practice sessions..
small hands would be closer to, levers..
suitably adjusted levers are assumed..
you should have a good 4" between inner
thumb and pinkie/ring finger, ie, inner bar
and front surface of levers..