The trap is practising both hands at once from the start and hoping they separate.
They don't — you get two half-learned parts. The bell has to become automatic first, because in
performance it is the part that never stops.
Bell alone, until it is boring. Switch the drum lane off above and play only the bell,
for minutes at a time, until you can hold a conversation over it.
Sing the drum part over it. Keep playing the bell and only voice the drum strokes.
This builds the relationship between the two lines without asking your hands to do anything new.
Add the drum hand on the coincidences only. Every column with an ochre underline is a
stroke where both hands move together. Two hands moving as one is not independence, and it is much
easier than it looks.
Fill in the rest. Whatever is left is bell-only — so it belongs to the bell hand, which
you already made automatic in step 1.
Drop the tempo far lower than feels necessary. Take the slider to 40–55. Coordination is
learned at the speed where you can consciously place each stroke; speed arrives on its own.
Practise away from the drums. Bell hand on one knee, drum hand on the other. Most of this
is a brain problem, not a hands problem.
Most players give the bell to the weaker hand and the
stick to the stronger one, since the drum strokes carry the dynamics — but follow whatever your
teacher does, because switching later is genuinely annoying.