Firstly to use a neck harness you must have one. I suggest a leather one, mine is branded Harbinger, and thus far it has done well over 8 or 9 years of usage. I bought nice unintentionally going with the old school style, and likely will never need to buy twice.
(The Spud Inc neck harness is often lauded online, I don’t like it. Spud straps? They’re the bomb. Spud neck harness? Go get an old school leather one instead.)
Now starting weight :
If you have never used a neck harness or worse you’ve never trained your neck (anyone who’s ever wrestled would be disgusted at you for being a pencil neck geek) I suggest starting with a 2½lb plate for 1 set of 25.
Build that up to 4×25 at a minimum, 4×50-100 being cool too, and then add weight.
When you’re strong enough to nod 20-25lbs x 50+ at all times I’d suggest just starting at a set of 50 and progressing until you’ve got a set of 100+ at that weight.
(I’ve done sets into the 300+ reps before.)
I’ll do the counted reps in the normal nodding manner, then let the weight swing front to back (like a kettlebell swing, but using the neck harness as the point of contact), and end with a static hold spine straight, and parallel to the ground as “extra credit”.
To keep from getting too stiff from the harness work :
1. If starting out gradually build into it.
2. Always do range of motion work after. I like using the front bridge from the knees going front to back, side to side, and “around the world”
Also, frequency is best for the neck. Train it daily or near so. However I’ll allow a rank stack of dimes sad excuse of a neck beginner to start 3x weekly or every other day as long as they build up the frequency as they become more developed of neck.
Persistence & Tenacity