I purchased my stencil from Cutting Edge Stencils. I chose the 'Beautiful Birches' large tree stencil. It was pricy at $90, but it came with several customizable options, like adding leaves and birds, and is reusable. I have already used mine twice since I changed the color of my living room a few months ago and had to re-do the mural.
I used acrylic paints, as I have found they work best. I have used regular wall paint in the past, but I don't recommend it. Wall paint is runnier and tends to bleed under your stencil. I also bought a stencil brush from Hobby Lobby that had gel holders so you won't get a callus from stenciling several hours. These were very comfortable when doing a large stencil project like mine.
Now, I was ready to begin stenciling. I placed the stencil on the wall and secured it with Frog Tape. If you've never stenciled before, just know the less paint on your brush, the better. I would dip my brush in paint, then wipe most of it off on a paper towel until the brush was dry before applying it. The drier the brush, the less likely the paint will bleed under the stencil. Always paint using a dabbing motion with stencils. After I finished, I carefully removed the stencil to reveal my new mural.
The birch trees were the perfect addition to my living room. I have received numerous compliments on them.