When I go to clip my cat’s claws, I do it when they are sitting up not lying down. They are not on my lap, they do not have their bellies exposed, they are simply relaxed and in a sitting position.
It seems to be a bit easier than when they are on my lap. First of all, some of my strays and ferals are not lap kitties. So I have evolved this process over time. I clip while they eat.
Lying on the floor near them while they eat, I take the claw scissors and gently using it as a probe, I expose their claws. One by one, I begin to trim off just the tip being careful to not expose their quick (the pink part of the claw where the blood supply is located). Because they are eating, they don’t mind their feet being messed with and the trimming goes quick and easy. I make sure to leave some meaty treats in their food bowls on claw trimming days, which keeps them occupied and chewing on something besides me. I don’t make a big deal about clipping their claws, and have just found this system to work best for me.