You should trim the pubic hair preferably with scissors before shaving.
You may even consider only trimming alone. But if you must shave, then trim first. Also endeavour to stretch your skin before shaving. And apply Aloe Vera after shaving. Some would recommend Hydrocortisone, but I'm not a fan of medications....I'm a fan of trimming :)
Unfortunately ingrowns are tough to avoid unless you trim only or have had laser hair removal. But here are a few tips:
trim first; hair shouldn't be more than 1/4"
use a sharp and clean razor
use moisturizing shaving cream
shave in the direction of hair growth
After you're done and are completely dry, apply antibiotic ointment (like Neosporin) to the ...