You can sharpen often for the best point. Save trees and money with sharpenable lead. Prepunched paper is much more expensive. Patience and precision while punching will be rewarded with excellent registration. When inking with pen, clean pen at every stopping point with ammonia and a toothbrush.
Dirty nibs are unreliable.
Hone or replace the nib frequently. Fresh nibs are easier to control and produce the best quality line. Good brushes for inking are quite expensive. Bite the bullet. They'll work better and last a long time if you do the following.