I learned how to interpolate between the marks in slide rule class in high school. When I got to college, the first physics lab was how to read a micrometer. It was an analog world back then and you had to know how to interpolate to get the extra precision. I have a B & S micrometer that has a vernier for tenths but I rarely use it. Every time I have checked my interpolation, it has matched the vernier. It should be stated that there is no additional precision gained by adding the vernier. The precision is built into the screw. The vernier just makes it easier to read.
Regarding interpolation, to gain experience by first just looking at the position between the marks. If it's halfway it' .0005" If it's nearer the low side than the high side, it's .0004" or less. Nearer the high side, it's .0006" or greater. If it looks like it's about halfway between the lower mark and the middle, it's either .0002" or .0003". Just a shade past the lower mark, call it .0001". If you have a digital mike or a set of gage blocks, you can practice with some known quantities. It won't take long until it is second nature.