Allow individual campaigns to determine what is so bad about being an elf or a dwarf that people would not want to play them despite the advantages. Each race description could give a few possible examples, with the Dungeon Master's Guide and individual game world supplements going into more details about how to determine these. That is, except for those characters who are already multi-classed. It makes no sense that an elf or dwarf should not be able to change professions during their long lifetimes. It is a great role-playing tool, that too often misunderstood as a limiting factor, but that is only the case when characters are played as superficial stereotypes.
Alignment creates great character motivation and inner conflict.
This just to help DMs, how many hit points do they have. And similar questions need to be answered. This also goes for monsters. Do not limit that by putting undue emphasis on any one place. Well, I have other opinions on monsters, magical items and treasure, but those are more personal beefs that individual DMs need to handle on their own.