I have just finished painting an acrylic portrait of a dog. Just for fun I took a few photos of the various stages, so you can see how the layers are built up.
In the first picture you can see a little of the original pencil sketch left. At the start I only draw out the bare minimum, and then layer up the paint in thinnish layers. With acrylics you can add quite a bit of water and the washes you can achieve are not dissimilar to watercolour paint.