Work bigger when your designing, you can always scale down later. Try using a lighter touch with the pencil. Using a harder leaded pencil may help you clarify your lines and keep the thickness of your lines under control. Take your time refining your lines.
See if any local colleges have a printmaking department, and sign up for intaglio printmaking, or woodcuts. Intaglio uses gravers on plates for printing. Woodcuts use woodcut tools also for printmakng but the hand/eye coordination skills are quite similar.