These are mostly sewing machine tips, not specific to Sergers. We're including them here for the useful reference information.
Sewing tips for swim: use a stretch needle. A small zigzag .5 width and 2 length. Go slow. Have fun!
A Teflon presser foot makes sewing Spandex that is sticky or slippery a breeze. Changing the foot can make all the difference as the Teflon sewing foot glides over the fabric and prevents skipped or loopy stitches.
Sewing Spandex & Lycra – Sewing Leotards & Swimwear
Melly Sews: Sewing Spandex Lycra and Elastane
SergerPepper's 30 Best Tips for Sewing Knits with Serger & Sewing Machine!
Spandex 101 Basic Techniques and Finishing
Including this great tip from thegeekyseamstress: