Here's my process and what I learned. Take what you will--this is just my experience.
I ended up using an inch and a half Master's Touch brush. I tried the sponge that's made for stencils, the high density roller that's also made for stencils and about a billion other brushes I had on hand. Nothing but the aforementioned brush worked for me. That's not to say they wouldn't work for you, but I think the combination of my plaster, uneven wall and the metallic, thin paint I used made for a disastrous pair. (For the record, I used Martha Stewart's Metallic paint in Bone.) Am I being dramatic enough yet? All that to say, the brush worked perfectly for me, but it took so much longer than if I'd been able to roll the pattern on the wall. Instead, I pulled the paint from each corner of each diamond shape into the middle so that the paint wouldn't bleed under the stencil.
Ok. Enough whining. You know why? Because I love my wall. Moving on.
You know what else I love? My brand new floor lamp (see the last image)! Geez louise, were we in need for some lighting in a bad way. This whole room has no above-head lighting so this beauty has recently saved the day.
MORE LINK LOVE FOR THE ROOM:
lamp, Fashion For Home | stencil | amber pillows on bench, World Market | kilim pillow on bench, Pottery Barn (sold out) | gold sequin chevron pillows, TJ Maxx | bench, Craigslist | couch, ZGallerie | ikat pillow, Target | black and white smaller pillow, Ikea | yellow and gray pillow, TJ Maxx | black and white larger pillow, Urban Outfitters (sold out)