Set up a dot grid for where the points of the letters are going to fall before writing them in. That's my primary secret to doing hand lettering with an actual pen. I also hand-letter some of my maps digitally, and that's a lot easier since you can erase until you're happy. Say you wanted to learn to do a font, you should try to copy its alphabet separately to get a sense of the shape of the letters where you won't hurt the ink in progress. Then you know where the extremities are going to fall, so you will set up a pencil grid appropriate to the letters you plan to write, and then pencil the letters, check it's okay and spelled correctly, and then ink the letters and erase any guidelines. Using a ruler to set up guidelines is how I learned to hand letter comics. You have to view it as drawing each character, not writing at all. Then you'll start to get it.