Write a day, not a description
Sitters follow instructions exactly when the instructions read like a day unfolding rather than an essay about the species. Start with the morning in working order: what time the lights come on or which timer to check, the temperature to read at the warm end and the cool end, what a wrong reading means, and the first jobs in sequence — water dish emptied, rinsed and refilled, yesterday's uneaten food removed, fresh food offered. Move through the afternoon and evening the same way, ending with lights out and the one last check you want done. Anything your reptile needs only on certain days, such as a bath, a shed check or a supplement-dusted feed, gets its own dated line rather than a vague instruction to do it sometimes.
Put numbers on everything the sitter can measure
A sitter who does not keep reptiles has no feel for what looks right, so replace impressions with readings and amounts. Give the basking-spot range, the cool-end range and the humidity range your animal actually lives at, and say where each sensor sits. Describe food in counts and sizes — three locusts roughly the width of the gecko's head space, a palm-sized pile of chopped greens — and state plainly what to do with refusals: remove it, note it, try again tomorrow, rather than leaving live food loose in the enclosure. Name the supplement routine by day, in plain words, and keep the tubs in the order they are used.
Label the physical kit
Half of sitter error is equipment confusion, so label the reality in front of them. Put a small tag on each plug and cable: heat lamp, UV tube, thermostat, timer. Write on the food tubs what is inside and where the spare bulbs live, and leave the spray bottle, tongs and cleaning cloth in one obvious place. Add a short list of never-dos written for your species and your home: never unplug the thermostat to make the lamp brighter, never tap the glass to get a response, never take the snake out to show a visitor, never use cleaning sprays inside the enclosure. These lines matter because a careful sitter improvises exactly where your routine has a silent rule.
Show one full round before you leave
Paper alone is not enough for an animal whose care is mostly observation. Have the sitter do one complete round with you standing back: reading the thermometers aloud, preparing the feed, misting to the humidity you want, spotting whether the animal looks bright or tucked away. That single rehearsal surfaces misunderstandings while you are still there to correct them, and it shows the sitter your animal's normal behaviour, which is the baseline every later judgement depends on.
Make the emergency path one line long
End the instructions with a short block the sitter can act on without thinking: the signs that mean phone you the same day, the signs that mean go straight to the vet whose name, address and number are written there, and your permission for the vet to treat in an emergency. Keep a copy of the whole routine inside the enclosure lid as well as wherever the sitter keeps their phone. Sharing the finished routine through a KinsLe Care Pass means your sitter holds the current version, with your vet and contact details attached, instead of an old printout missing the one change you made this season.