Unsteady hands get the blame for bad drawings, but the problem is usually where you look. Glancing at the paper constantly means drawing what you think an object looks like and not what is in front of you. One exercise trains the fix, and a mug and a pen are enough.
Your first day
Starting takes ten minutes with a mug and a pen. Any pen that doesn't skip and any paper works. Expensive materials mostly just add unnecessary stress before you need them. Set a mug in front of you. Start anywhere on its outline and keep the pen moving slowly, tracking the actual edge of the object with your eyes and not looking at the paper until the line has gone all the way around back to where you started. It will look distorted, and that's expected, but notice how often the parts still sit in the right places relative to each other. Don't lift the pen even when the line goes somewhere unexpected.
Glancing down at the paper constantly to check the drawing is the habit to avoid. That's what produces the stiff, overly careful lines beginners dislike about their own work.
You're done when the line has gone all the way around without you looking down.
The thing most people miss
Drawing well seems to need a steady hand, so shaky lines feel like a sign of not being good yet. In this exercise the wobbly, uncertain line usually captures the mug's real proportions better than a careful, constantly checked one, because your eyes did the work and your memory of what a mug looks like didn't.
Doing this kind of looking-heavy drawing first makes the drawing that follows looser and more accurate.
How you'll know it's working
With repeated tries, a line drawn without glancing down will match the object's real shape more closely than you expect. Keep your first attempt and hold a later one next to it, and the difference is easy to see.
Eventually, looking this closely at an object stops feeling like an exercise and starts feeling like just how drawing is done. From there, basic value shading, using darkness and lightness instead of only outlines, is what starts giving these same loose lines an actual sense of form.