I wanted to share some tips that helped me, so that hopefully they can help someone here.
Tip 1 (the most obvious tip probably): identify the reason you pick at your nails/hands.
For me, it was a sensory thing. I pick a dry skin, broken or snaggy nails, hang nails, rough cuticles, etc.
Once you identify the why you can formulate a plan for yourself.
Tip 2: formulate your plan
Telling yourself "don't pick" won't work. What will work, is finding what prevents you from picking in the first place. For example, if you pick at your hands because you need a physical release for anxious energy, get something you can put that energy into. Fidget rings, rub strips, etc.
If you're like me, and it's more of a sensory thing, work to prevent the sensory issues. It'll take time and effort, but it will help.
Tip 2.5: take progress pictures and keep a log/journal of your triggers.
Knowing your highs and lows will help you better find a system that works for you. Everyone is different and progress is rarely linear.
Tip 3: intentional practice
You're breaking a habit. You're going to need to put some effort into being intentional about what you do, especially early on.
If you're curious for what I do for tip 2: I have a hand car bag I keep with me everywhere I go.
Basic items that I always rely on:
Nail File
Nail trimmer for hang nails
Nail oil and hand cream
Religiously using nail oil and hand cream helps prevent hang nails in the first place, but if one pops up, I have the tool needed to remove it without pulling or picking at it.
Also, nail file to smooth out any roughness with my nail edge.