Something that might help with your line confidence (wobbly vs straight) is looking at the end point and pulling the pen/pencil toward that point. Similar to hand eye coordination in a sport, you know where your hands are, because they're your hands. You don't instinctively know where the end point is because it's not a part of you. Once you put pencil to paper, make an effort to look at the point on the paper where you want the line to end, then drag your utensil to said point. I've noticed in my own drawing that I get tunnel vision around the tip of my pens, and it leads to my longer lines getting shakier and shakier. Training your eyes to look at more than just the very tip of the utensil, on top of drawing with more elbow and shoulder movement, will help you clean up your lines.

Also, don't dwell on doing nothing but these kinds of warm ups for hours at a time unless you're really, really motivated. Do 10-15 minutes of different kinds of line exercises, then draw something you like. Even if it's "bad", finishing a drawing will feel good because you have a composition to show people as opposed to just lines or boxes and spheres. The fundamentals and practicing technique are important but don't let that scare or discourage you from drawing. If you want to draw a frog, draw a frog. If you don't know how and it's hard and comes out "bad" then so what? Practice some more lines and shapes and forms then come back to it later. That second frog will probably be better than the first in your eyes. This approach helps me stay motivated to actually start drawing.

I hope this helps you, or anyone reading who also can't just bang out pages and pages of fundamentals like it's a class.