A young person in the community has six ewes and asked this question. After 2 lambing seasons. we're old-timers.
1) Increase feed grains for ewes as the time comes close, eight weeks or so out, to help the lambs make weight in the uterus. Oats are good, but in Maine you need selenium supplement, so a sweet feed with vitamins, minerals including selenium, should be part of the mix, or they should have a sheep/goat protein lick available with selenium, or they need shots of selenium (Bo-Se brand is the norm).
2) Related to selenium deficiency, read up on White Muscle Disease (WMD).
3) Pregnant ewes need Clostridium sp. vaccine (Tetanus vaccine) four weeks or so prior to parturition, or best guess. While giving the shot (subcutaneous), trim surplus fleece from vagina, and check for the udder getting bigger and firmer ("forming a bag"). Good time to trim hooves, too. Handle them carefully to avoid miscarriage.
4) Sort out a restricted lambing pen ("lambing jug") to separate ewes and babies, and ewes close to their time. Put in a heat lamp. It's too cold in Maine not to have a heat lamp. Four by five feet is a good size.
5) Make up a kit of emergency items: colostrum replacer, bottles and nipples, intubation kit for reviving lambs, extra heat lamp bulbs, Blue Cote, shears, elastrator and bands for painless castration.
6) As the time comes, watch for bulging sides in the ewes, ewes forming a bag, ewes pacing or making nests, or obviosuly uncomfortable, off their feed
7) If you think the baby is coming soon, separate the ewe in the jug, moving her gently
8) Keep checking ewes in labor during the night. A cold lamb can die while you sleep.
9) Lambs are usually born easily enough, but read up on the ways they can be turned around in the womb, and try to figure out the remedies just in case
10) When born, strip the nipple of the wax plug and, milking the ewe, squirt some milk to check it's there. If the lambs don't feed soon, put the nipple in or close to the mouth and squirt some right in there.
11) Make sure the new born lambs find and get under the heat lamp.
12) Bo-Se shots and tetanus vaccine are good to give to lambs as soon as they're strong enough
Otherwise let nature take its course. Enjoy!