As children we spend hours practicing how to write our letters -- upper and lower case, manuscript or cursive. Then, we move on to putting those letters together into words and then full sentences. But these letters and words are always written on lines. For some people it remains a challenge to write in a straight line when these lines are not present. Luckily, if you find yourself in a situation where you must write presentably on a piece of paper that does not have lines -- addressing an envelope for example -- there is a simple trick that you can employ.
Place a lined index card inside the envelope, making sure the lines of the card face the front of the envelope.
Lay the envelope on a flat surface and apply pressure to the envelope until you can faintly see the lines of the index card through the front of the envelope.
Use the lines of the index card as a guide for writing the address onto the envelope.
If your envelope is made of thick stock that will not allow you to see the lines of an index card through it, simply use a ruler and a pencil to draw four straight lines in the front centre of the envelope where the address will be written. Then use a pen to write the address, and erase the lines.