I have found some doubles practice like the game 27 or Round the World to be very helpful.
However I invented this routine/game/challenge to penalize the thrower for splitting or straying. The game encourages you to throw a marker to guide.
It is a work in progress so any comments or suggestions are welcome.
Basically you get a cross X if you split the double, stray into a neighboring number or miss with all three darts. You get an "O" if you hit the double and move on to the next number. Any darts you have left in your hand can be used as free shots for the next number. You can only get 1 "O" and a maximum of 3 "X" per throw.
e.g XXX split, miss, split. 2 X for each split and 1 X for missing with all three darts.
Starting at Double 1: 1st dart = split: 2nd dart outside 3rd dart = D1
D1 XO
Then on Double 2 1st dart = D2: 2nd dart shooting for double 3 = split 3rd dart(No Penalty) = D3
The board should now look like this
D1 XO
D2 O
D3 O
On Double 4 all three darts go outside the wire
D4 X
Move to Double five you split, go into D20 and miss(3rd dart) = 1 X each
D5 XXX move on to double 6
Continue to the bull
Double bull = O
Single bull = Miss
Outside = X
At the end of the game add up all the X subtract all the O if you are in negative numbers well done.
D1 XO
D2 O
D3 O
D4 X
D5 XXX
D6 XXO
D7 O
D8 O
D9 XXO
D10 O
D11 XXX
D12 O
D13 O
D14 XO
D15 O
D16 O
D17 XXX
D18 XO
D19 XXO
D20 O
BULL XO
20 X - 18 O = +2
You can play the same kind of game on triples. e.g. "O" = Triple 20, Miss = Single 20, "X" = single 1, triple 5 etc. I'd only go 10 to 20 for 501 or less if you play cricket and end on the bull.
Hope this makes sense
Game is called ZAP XO
