Improve line control by... making lines. Look around the kitchen... find a ticket stub, an envelope you received, a tea bag and a magazine. Focus on details rather than big picture. The fonts on the ticket stub, the alignment of letters on a postmark, the logo on the tea bag, the UPC code from the magazine. Take a large piece of drawing paper and draw wavy lines to divide your paper into a bunch of sections of various sizes. No measuring! Grab a pen or marker. I like to use PITT pens or Sakura microns and colorize with Sakura gellyrolls or PITT brush pens or even watercolors. But just as much, I adore Papermate medium point pens.
Scope out interesting fonts on product packaging in your pantry, a simple children's toy, find a pattern on a sweater or wallpaper or fabric. Keep moving forward. If you find yourself waiting in a doctor's office, at a cafe, at the airport, in your hotel room (although more fun to try this in the lobby), look around. 99% chance there is something to draw. A gum wrapper, a receipt, the title page of a book, a gift card, coffee cup, advertisement, a packet of sugar. Just the text, logo or design, not the entire thing. So maybe the logo on the corner of the cereal box, not the entire 3D box. Get it? Notice how characters align left-right and top-bottom. The serifs on the fonts, or lack thereof. Give it 1/2 hour. Later, rinse, repeat another day.
And... if you haven't tried it, carrying a camera with you (looking for interesting things to photograph) will help you notice patterns and details, interplay of colors, light and shadow. Often things you would not have otherwise noticed. Check out Collection for more.
More ideas for pen & ink...