Fix the tablet pressure and other things that are included with the tablet. Depending on the quality of the tablet, the better the lines will be. If the tablet is working perfectly, then you only need practice.
You need to do a LOT more practice. One day is not even close to enough. It's more like you're learning to draw for the first time again and you need a few months, at least, to get a better hand on it. The first step to improve is to go back to the basics and just sketch. You're not ready to start making fully finished drawings and you should not start a drawing without sketching it out first. That's how most people end up with messed up proportions and such. And the sketching lots of things will help you a lot with that hand coordination problem.
I used to be like that too! My suggestions are that:
*PRACTICE I swear, at my first try on tablets, it looked like some kid's drawing, but as you progress, even if just for hours, you'll get a hang of it soon! Just draw,draw,draww!
*Scan? I never tried this option but i'm more comfortable with coloring with my tablet than drawing, weird, i know. However, try drawing your lineart on paper first then scan it then use it as your line art!
There's a tutorial here in DA that excellently explains how to turn your scanned LA to LA digitally :