First we teach "color in the lines." Not long after, we are teaching five-year-olds to write in the lines. I teach my class by comparing the lines to a two-story house. All adults (uppercase letters) and teens (tall lowercase letters) stand downstairs, but are allowed upstairs, too. Babies (lowercase letters) are not tall enough to go upstairs and have to stand downstairs. Then, there are five brave babies that aren't afraid to play in the basement (lowercase letters: g, j, p, q, y).
We also practice lowercase letters with a Dr. Jean song, which has slipped my mind, by doing something up high, in the middle, or down low when you say each letter of the alphabet.
Finally, I make shape-boxes around words to help the students notice words have a shape. Some catch on quickly, others... well, don't. ;)