If you're interested in investing time into improving (it's hard to tell based on your comment alone) it sounds like https://drawabox.com/ (it's free) starts with just what you're asking for -- how to make straight lines on a page. A big part of the first lesson is practicing how to make confident, accurate strokes using your whole arm.
Cool, thanks. Yeah, I'm pretty sure there's something fundamentally incorrect about how I draw, even though it feels fine (but the results are terrible).
