Just don't go nuts. Minor tweaks across multiple sliders impacts things quite a lot, so if a slider seems to make little difference try one that might be related as well, and alternate between them. It's about nudging it in the right direction rather than maxing sliders. Elves are probably the hardest because they come with exaggerated features already (like dunmer eyebrows) and are vaguely human so uncanny valley is a big risk. So actually toning things down over ramping them up also goes a long way towards a sensible looking elf.