All you'll need is a tray, a can of chalkboard paint, and a foam paintbrush (the bristles on a regular paintbrush can leave streaks). The tray pictured here started out as a frumpy $2 tray with a flower painted in the center of it. I added a little chalkboard paint, and now it's "tray" chic! Get it? Tray? OK, moving on.
Start by selecting a tray. Just about any tray will do. Chalkboard paint adheres well to most smooth surfaces, but I've found that really shiny surfaces, such as glass, don't take the paint well. If you don't have a tray, you can make one by adding 2 handles to the short sides of an ornate picture frame and cutting a piece of foam core poster board to use in place of the glass.
Paint a coat of chalkboard paint over the flat portion of your tray (or on the poster board if you are using a homemade tray). In most cases, there's no need to prime first. Allow the first coat of paint to dry for 24 hours, and then add a second coat. Once the second coat has had 24 hours to dry, your tray will almost be ready for your message. Before you write on it, condition the chalkboard by rubbing the side of a piece of chalk over the entire surface once. Rub clean with a soft cloth, wipe down with a damp rag, and allow to dry before you write on it. This will prevent the "ghosts" of previous words from haunting you after you erase them.
The truth is, I'm nuts about chalkboards. For more fun chalkboard ideas, have a peek at this article that I wrote ages ago before the dawn of my blog.
This post is also linked to a bunch of neat DIY chalkboard projects at Reinvented.