The biggest mistake most of my students make is not changing the needle often enough in their sewing machine! You will get a better stitch and less puckering with a new needle. Needles develop burrs and slight bends as you sew, so change your needle after about 10 hours of sewing or at least with every large project. Don't wait for it to start making a clicking sound (that's the sound of the needle hitting the hook and can damage your machine).
Always match your needle to the project - the weight and type of fabric you're using and the size thread. Knit projects should be stitched with a ball-point needle. A universal needle is actually between a sharp and a ball point and can be used for many types of fabrics. However, with cotton woven fabrics I like to use a sharp. In fact, when I make my purses I like to use a Jeans/Denim needle.
