The first thing to do for skipped stitches is to replace the needle with a brand new one. Use a good quality needle that is designed for the fabric you are sewing. Schmetz is my preferred brand.
Schmetz Universal needles are good for general purpose sewing on most wovens and knits. If you are sewing heavy fabric try a Denim needle. If you are sewing elastic or lycra try a Stretch needle.
Remove the needle plate and the bobbin. Clean the bobbin area and add a couple of drops of oil.
If the above doesn't work, the machine timing is likely off. Sometimes, if the timing is only slightly off, you can fix the problem temporarily by using a Stretch needle because it has a longer point.
PS Sorry, I haven't yet found a web page with detailed info for timing a sewing machine.
J Korte, April 2006
