Skipped stitches are usually down to a damaged or incorrect needle type or size.
Changing your machine's needle needs to be done at least every 6-8 hours of sewing!
For general use, universal needles in sizes 60-120 are available. These needles are a bit ballpoint (used for knits) and a bit sharp (used for a woven fabric). We recommend changing your needle according to the type and weight of the fabric (and thread) you are using. Schmetz has an information booklet that you may find helpful. Click Here