Shetlands may be different to my Jerseys, but with the Jerseys here's what I'd advise.
Firstly, yes, establish a routine which she will learn as her 'let the milk down' signals. Udder washing is a good thing to do from this point of view, as well as for hygiene!
Secondly, sometimes a heifer doesn't realise to let the milk down for you - to teach her, one thing you can do is do your pre-milking routine, then bring the hungry calf round. She'll let down for the calf; you get on and milk some out while the calf is suckling. You may get so much slobber over you and in the jug/bucket that you don't want to use it, even if the calf doesn't bunt it over while you're working under her
, but don't worry about that, you're just teaching her to accept your fingers milking her as normal, and to let the milk down to that routine. (If you have some pigs, you can give them the spoiled milk. Or chickens. Or dogs, or whatever.)
Another tactic which works with a recalcitrant Jersey is to give her her cake a handful at a time. A bit to get her tied up and while you wash her / prepare her. Then a handful as you start. Then no more until she is doing what you want, be it standing quietly while you pull away, or dropping the milk so you can start. However, be a bit careful with this approach; I've taught my one Jersey to let down
after she's eaten the first bucketful of cake!
(She is a particularly intelligent animal, mind. Her daughter was a doddle compared to her!)
Other things you have probably already tried include massaging the udder, doing a human version of the calf's bunt, wetting the teats like a calf's mouth would.
I haven't milked goats, but some of the things goat people say about how to milk a goat make me wonder whether it's a slightly different technique... anyone who handmilks goats
and cows able to comment?