get on a nearby hill or rock and kill ones you don't want as they usually spawn in 2s or 3s (recommend an argentavis). then start shooting the mammoth with tranquillisers. when it torpor runs finish it off, they are very slow so very easy to hit. (protect from dire wolves, yutiranus, etc....)
If you have a tame they you can ride and shoot off from you can use to tame a mammoth. If you have a tame that has a knock out power especially a equus would be great to also help knock out but be careful not to hit once knocked out because it can ruin the taming effectiveness.
Use carrots or anything the dododex suggests to use to tame. Have narcotics to knock out, and tranq arrows.