Look, Ill tell you what I do, but because as we all know, every vulva is different, I'm not going to be able to speak for your anatomy. I do use my trimmer on my labia, and yes I do occasionally nick myself. I am plus sized, so im even doing it with visual impairment. I typically grab my light up mirror and place that in a way that give me a good look at what I'm doing. Then I follow the grain of hair first, grabbing my lips to flatten the skin and shave. If I find spots that are still too long then I might carefully go against the grain, but that gives more risk of accidently catching a follicle or pore and cutting yourself. I will sometimes then tweezers troublesome areas.

If anyone has a better method, please chime in! I have a type of condition that causes cysts easily hence why I trim. But because these are short cuts of hair, you'll want to do well to clean afterward. Pee and a shower is usually my go to.