Skinning

Skinning is an excellent support profession for leatherworking. Train this skill, purchase a skinning knife, then simply right-click on beast corpses to skin them. You'll be able to support your leatherworking and keep yourself in good armor at least for the lower levels without any particular effort.

Currently corpses need to be completely looted before they can be skinned. This is annoying and I hope it goes away, but it hasn't yet. You can skin other people's kills as well as your own.

Your skill increases may stop rather dramatically at some point - you've reached the limit of what skill the level of mobs you're fighting can give you. You'll continue to get leather, and your skill will continue to increase once you start skinning higher level mobs, assuming you haven't capped out your current skill level (apprentice, journeyman, etc.)