When using the ladder method, do you load 1 bullet at each powder increment or do you shoot more than 1 at each load ?

1 bullet! You are looking for a load where a small variation in powder charge (eg. 0.2 grains) does not affect the bullet much.
Peter.

I usually load 4 or 5 at each level, in one grain increments. I will generally only shoot 3 of them. I'm usually checking for velocity and accuracy at the same time. Testing 1 at each level really wont tell you anything, unless I'm misunderstanding what you're trying to do?

I always shoot 2 of each if the rounds are expensive and 3 if they are cheap.

I tend to go in .5, 1, or 2 grain steps depending on the case size. When I think I see a sweet spot I'll load a finer step series around it.

.1 grain is an awfully small step!

The Audette methiod (ladder methiod) is done at 300yd (preferably), the target is tall & narrow with a single aiming point. One round of each powder increment is fired, and (in theory) you will find that while most of the shots string fairly evenly spaced vertcly, there is usualy a cluster of 3 or 4 shots together. The center (powder charge) of this cluster is the most forgiving of round to round powder charge variation.
It's a little more involved than that, but that does cover the basics of the methiod. See also "Optomal charge weight" theory, which is a modified Audette methiod.