Experience will help in deciding when to intervene and when to leave alone.
One rule is if there's been one that took some time / needed a lot of help, you don't want any that are behind to be kept waiting much longer, especially if you know / suspect there are three.
I find that most of the problems with mothering (including lambs which don't thrive later on, which is a more subtle one to spot and harder to be sure of the reasons) arise from too much intervention. So unless I think a lamb or ewe is struggling, if I have any concerns then I will just check that the presentation is good and then let the ewe try a while longer.
And assistance with one that's just taking time / the ewe is a bit tight, I will try first to help by applying supporting (pulling but not excessively) pressure when the ewe is straining, and then just holding the legs steady until she strains again. Only if after maybe three or five good contractions no progress is occurring will I pull any harder. If it's the vulva that's tight (usually only with a first-timer), I gently work on stretching the vulva around the head with a very well-lubed hand. My experience is that the more the ewe was made to deliver faster than she wanted, the more likely are mothering problems.
If it's the shoulders which are sticking, then often pulling one front leg fully forward will lengthen the shoulder joint sufficiently to allow the shoulders to come.
If it's hips/rump which are sticking, you will need to help, but take care that you don't bruise the ewe. So again, pulling as she strains, then just stopping the lamb from going back in and letting the ewe rest before the next contraction.
Make good notes about who had what problems and what you did. Then after they've all lambed and all the families are out and happy at grass, review your notes and look for clusters. Then think about why those clusters had those problems, and think of some changes you can make next year to reduce them.
For instance, we had one tup whose lambs on one batch of ewes were all too large. On all the other ewes, no problem. So we didn't pair him with that batch of ewes again.
If all the lambs are overlarge and you fed cake before lambing, feed less next time. If all the lambs are overlarge and you didn't feed cake, and the ewes weren't on overlush grass, don't use that tup on those ewes again. And so on.
If all the ewes are lacking enough milk, give them better grass next time if you can, otherwise some cake. (But calibrate for conditions - it's been stupid wet this year, so the grass won't have been as nutritious as it would be in a drier year, etc.)
