I'm likely wrong, but I can't recall reading a post about exactly what it will feel like, on the lever, to pull a successful shot. I don't mean placing the thing on scales; i just mean how roughly to go about using the right amount of force throughout the pull. I'm no expert but i thought this might be of use to anyone who is in the position i was in, trying to improve with a naked pf, a few months ago.
My thoughts on the force required are, that with experience you will get to know, for a grind&dose&bean, the force required mid-pour. My advice is to use that same amount of force STEADILY from the very outset. As the flow appears, and then as you reach mid-pour, reduce the force so as to maintain the flow rate.
This would have helped me a while back: i was never certain whether to use more, or possibly less, force before the first drips appeared; and i suspect poor lever consistency was responsible for non-uniform flow from my naked pf.
As i say, i'm no expert, but my shots are pouring well and tasting great.
However, if i'm contradicted by someone with greater experience, well i'm open to suggestions and ready to learn too...