I trim off the real bushy body of my pubes with a pair of hair scissors first, then when there's less jungle to fight through stretch the nutsack out and very gently run my shaving razor across it.
I use something like shaving oil or argan oil rather than shaving foam for my nuts. Shaving foam is too dense for how bumpy and wrinkly your sack is, even stretched out: you'll just miss all the hair or if you press too hard risk cutting your nuts. Using oil lets you see what you're doing and will help your razor glide across the sensitive skin while just taking off the hairs.
Be extra careful with the scissors. I've never nicked my balls with my razor but i have occasionally put tiny cuts in my sack skin by catching it between the scissors blades when getting in close. Aim carefully and close the scissors slowly rather than snipping them shut quickly, so if you feel them pinching you you can immediately ease off rather than hacking a wound into your scrote.
What do you use?