Check your garment after you wear it every few times. The sooner you clean makeup off, the better the results. (Wearing a scarf around the neck is a major step towards a clean collar!) Your best solution for smooth leather is to use Aquila Leather Cleaner! Just spray and wipe. Let dry 15-20" and repeat if desired.
If you do not have Aquila- wipe the surface with a damp lint-free cloth. You can use clean water or a very diluted solution of mild soap, like Ivory or Woolite, to dampen the cloth. Do not scrub. Wait 15-20” for it to dry and repeat if necessary. Moisturize and protect.