There are so many ski pass options, you need to think about this in advance. Check out the ski pass website as soon as you have booked your apartment. You can get the passes posted to your home, saving you from queuing to buy them on your first day skiing.
The first question you need to answer is: do you want a pass for just St Martin / Les Menuires, the whole valley, or the whole Three valleys? Meribel is so readily accessible from St Martin de Belleville, even for learners, that I’d say get the whole Three Valleys. The added enjoyment will rapidly outweigh the small extra cost.
Then you need to consider group passes: For two (Duo), three (Tribu) or a family (four or more, at least two children under 18).
If you are skiing for more than 8 days in the year, consider the Liberte pass. This is a pay-as-you-go card, direct debited from your account, as-and-when you ski. I love it, although it does encourage you not to ski on bad weather days at all. You have to buy this pass online, before you come out to the Alps.
The ski pass shop in St Martin is next to the Bubble, a couple of shops to the right of the Dahlia bar. The queue does get quite long at 10 a.m. on Sunday, when everyone is getting their passes for the week. It shuts around the time that the bubble does, so you can’t nip over in the evening. If you don’t get the passes on the web before you come, I suggest you find someone prepared to get up early and walk over for 9 a.m., across the piste.
Carré Neige often gets offered when you buy your ski pass. This is a ski-insurance cover you can buy for about 20 euros per week. If you haven’t checked that your travel insurance covers skiing, it might be a small price worth paying.