If you've trouble painting thin lines, try revealing them instead of painting them. Start by painting a background color in the color you want the lines to be (in the example in the photo, this is black). Let it dry completely then paint the overall color (in the photo: gray in the background wings and white in the foreground ones).
While the second layer is still wet, scratch through the paint to reveal the underlying color. A pencil works well, as does a toothpick. Technically, it's called sgraffito.
Tip from: Tina Jones
A foam brush is best to use for straight lines, such as a distant ocean line. Angle the straight edge of the brush into the paint, then apply it to the canvas. I find it most useful to be able to follow a lightly drawn pencil line.
Tip from: Fallon Barker
When I use masking tape on an acrylic painting to get a clean line, I seal the edge with transparent gel medium. This makes a perfect edge.
Tip from: Susan Clifton
When trying to paint thin lines for a wire fence or telegraph wires in a dry or wet painting, just thin your paint down and use a pizza knife.
Tip from: John Brooking
In my opinion, oil pastels with oil paint and watercolor crayons with acrylics and/or watercolor represent the easiest and best way to in corporate line into paintings.
Tip from: Jon Rader Jarvis