|Photo by Ericka McConnell for Sunset Magazine - Styling by Miranda Jones|
How to: Make sure your deck is clean - hose down and use a wood cleaner to ensure there is no grease or mildew (if there is it won't grab the paint well). If the deck is already painted, you may need to strip or sand - check with your local hardware store rep. (Some may suggest a light sanding at this point). Use a porch paint (which is meant to handle exterior conditions). Let dry.
For the stencil - Using a contrasting paint, grab your favorite stencil design (there's some great ones at stencil-library.com) or make one using paint tape. Here is a video on how to apply tape for painting which could be adapted for stenciling. The paint tape procedure would definitely be faster and most likely what was used for this project. It might be best to establish a straight line at this point (a chalk line is a good technique for this). Then align the tape or stencil against the straight line. If using the tape procedure, you can just start to paint in between the tape lines you've created for your design. To paint use a stencil brush, a sponge or foam roller (which is faster for covering large areas) and dab the area being stenciled making sure the brush/roller is quite dry - so that it dries faster.
If using a stencil, either tape it down (with masking tape) or stencil adhesive (you also may be able to just hold down the stencil too, depending on the intricacy of the design). Align the stencil to your straight lines. Then start to paint using the instructions above. If you're repeating the design several times - cut out tiny marker (registration) holes in the corners of the stencil this will help when you reposition the stencil so that it's always the same distance from where you've just painted. Here is a link to a video on how to stencil.