|Sometimes you find fabrics which do not ease very well using the "two rows of basting stitches" technique. Even the tiniest bit of gathering causes puckers and tucks. Try this instead: Using a regular stitch length, stitch just inside the seam line (eg. at 1/2" if you have 5/8" seam allowances). As you stitch, hold or "crowd" the fabric by holding your finger at the back of the presser foot. The fabric will appear to gather up between your finger and the presser foot. Increase needle tension if necessary to get the fabric to ease. Sew sleeve into armhole as usual.
The first time I tried this I was skeptical but I was amazed at how much was eased in, with no puckers at all.
Sandra Betzina is very fond of this technique on her television show and in Power Sewing Step-by-Step.