Test your onboarding as if you were the new client
It's easy to lose track of what your onboarding actually feels like once you've built it and moved on to other work entirely. The only real way to check is to walk through it yourself, from the outside, as if you were a stranger signing up for the first time. I do this walk through on my own process every so often, and I always find something I had stopped noticing.
Sit down, open every link, fill out every form, and read every message exactly as a new client would encounter it. You'll catch things you'd never notice from the builder's side — a confusing instruction, a broken link, a message that sounds colder than you actually intended it to.
Do this walk-through every so often, not just once. Onboarding flows drift over time as you add new steps or change tools, and small gaps creep in without anyone noticing until a real client happens to hit one.
Try this today: go through your own onboarding process start to finish as if you were a brand new client, and write down every point where you got confused.