I remember being thought in a Rapid Viz class. We got a sample of a "typical" ID handwriting in all caps and we had to do the whole alphabet on 18x24 sheets. At the end we had to turn in a perfect sheet with the whole alphabet. We had to draw the parallel lines in pencil to guide us and then black ink. I think the key is in the stroke and consistent construction of the letters. Found this online.
Look up Architectural Handwriting and you'll see some variations.
ID handwriting is based on that but with some flair...a little slant, custom letters, more dynamic strokes, etc. With time you can develop your own custom style..the way you make your E's, W's, Ts, etc.
Repetition and really paying attention to the stroke was what helped.