Cross posted with Sally but I'll send anyway.
How many ewes are you lambing Jon? Will they be lambing in the field or indoors? When are they due to start? Are they first time lambers, or just you?
It's a good idea to do a 'wheel arch' trim on the ewes now to make it easier for lambs to find the teat on a woolly ewe, plus a dagging around the bums if they're at all mucky.
Straw up any shelters, with chopped straw if possible, as the long stuff will get tangled around the ewe's legs as she turns and turns just before she lambs.
Read up plenty before you lamb, not the obscure things which could go wrong, because that's what vets are for, but to discover what a routine birth looks like, and how quickly or otherwise it proceeds, then how long before the afterbirth should appear (and what to do if it doesn't)
Unless you're desperate to go that route, the lambs shouldn't need any meds at birth if they're outdoors, except immediate 10% iodine to the cord, dip is better than spray (mint sauce jars are perfect

). You might want to worm the ewes while you have hold of them, and do a foot trim (once the ewe and lambs have bonded and fed).
If you have more than a handful of lambs and you intend to register them, you may want to put in temporary mini eartags so you can tell them apart. The permanent tags are far too heavy for baby Shetlands. Poultry wing tags are perfect, and don't require an applicator.
You don't have to castrate any males unless they will have to stay with females beyond 4 or 5 months. If you do castrate, you must do it within 7 days of birth - Shetland lambs have tiny testicles so you are unlikely to be able to get them trapped inside the ring in the first few days. Whatever, make sure you have tried this out, or at the very least watched it being done several times, before you try it yourself. Have a sharp penknife with scissors (SAK) at hand for when you get it wrong so you can remove the ring promptly.
I really wouldn't bother with birthing ropes - we got some for our first lambing, over 20 years ago, and we have never used them. Again, that's what vets are for. Ditto stomach tube - dangerous to use if you don't know how.
So for my working list of lambing stuff:
10% iodine
rings and applicator
Latex gloves for general hygiene
Ready to use colostrum in a feeding bottle (from agric store) If you do need to use it, remember to cut a small hole in the end of the teat. If you don't it will last a couple of years unopened.
Antibiotic plus syringes and needles - our vets stock one lambing AntiB each year, so all shepherds in the area would be using the same, then change it next year. They would want to know you know how and when to use it.
Old towels etc for holding lambs which can be remarkably slippery.
Baby wipes for all sorts of stuff
Binoculars if lambing outside
A bucket to carry everything
Notepad in a ziplock bag (for when it's raining) to take notes of each birth, date, sex of lambs, eartag number, tick for lamb has fed, etc
Patience so you don't go barging in too soon
Alertness so you can spot if something has gone wrong straight off so you can react quickly