What will make it more or less precise will depend on the design.
If the printer you have in mind is one of those kits that you assemble out of plastic joints and metal rods, then stiffening the frame will lead to better repeatability. All the resolution in world means nothing if the machine isn't stiff enough to have good repeatability. The belt drive systems likely aren't that good either for repeatability.
If you can show that hysteresis and general repeatability are better than 1/2 the smallest step size, then a higher step count stepper may help. I'm guessing that a stepper connected to a belt in a flexible frame does not have repeatability good enough to warrant a fancy stepper.
Controlling the feed to the extruder will have an impact as well on repeatability. If the extruded material doesn't have consistent width or height then of course you can't claim a repeatable process.
If you're really just starting with building machines, then go build one, get it working, learn a lot in the process, and use the knowledge you gained to build a better one. You can't get good at something on the web.