CarlaC from Scientific Seamstress shares a downloadable pattern and tutorial on her blog showing how to make a t-shirt for an 18′ doll. The pattern has pieces for both long and short sleeves. Her tutorial gives tips for controlling the stretch of knit fabric and reordering your steps to more efficiently sew on a small scale. My daughter is super into American Girl dolls, so I can see this quickly becoming one of my go-to patterns for dolly clothes. Get the pattern and tutorial.
[photo from The Scientific Seamstress Blog]