You need different size needles for different fabrics.
I was sewing a purse handle the other day and kept getting skipped stitches. Re-threaded the machine several times including the bobbin. Cleaned really good. Then finally read the manual for troubleshooting. My needle wasn't big enough and once I put a larger needle in, my machine sewed perfectly.
The manual that comes with your machine should have a reference list for matching fabric with needles. If you don't have a manual, look online, there are lots of free manuals online.