Not stitching:the first thing to check for in this scenario is the threading on the upper and lower bobbins where you simply rethread if that is the issue. If not then check to ensure that your hand wheel is tight in case it was loosened while winding the thread on the spool. Another possible instance is that the thread may have unthreaded immediately you stepped on the pedal because you did not pull enough fret to the back of the machine.
Zigzag stitch sewing machine troubleshooting:trouble making a zigzag stitch is basically associated with the presser foot. You need to check that you are using the right presser foot whenever you intend to make a zigzag stitch. The zigzag stitch needs the presser foot to have a wider hole. Anything less will most likely mess up the zigzag stitch and even break the needle. Goes without saying that you should avoid this eventuality because if the needle breaks you might get shattered needle parts shoved into the sewing machine which is a recipe for further mechanical problems. To change the footer click the release lever, and remember the wider the zigzag stitch the wider the footer hole needs to be.
Skipped stiches:for sewing machines that skip stitches the problem is almost always with the needle. In most cases the needle might be bent or damaged. Sometimes the damage may be so minimal that you may not be able to observe it. Causes of the damage may vary ranging from; improper installation, using the wrong needle size, using the wrong needle type or accumulated fluff (for this a little cleaning would suffice). So just so you are sure before checking this possibility off try using a band new needle.
In other instances your speed might be affecting the stitching, thus let the machine drag the fabric at its own pace. You could add a table in front of the machine to catch the fabric so that you can reduce the pull tension caused by gravity on the other end of the sewing machine table.Also make sure that the thread thickness matches the needle type (for instance heavy duty threads go with the bigger needle, and thin needles go with lighter threads).
Bird nesting:(another name for jammed stitches) is a basic sewing machine stitching issue caused by failure to properly thread the machine. To determine if it is the upper or lower section that needs rethreading choose different colors for each thread and some scrap fabric. Now make a try to make a stitch and you can easily identify which color is jamming up stitches. However, in most cases the upper thread is the source of the bird nest. This is because the sewer may miss putting the thread through the take-up lever which forms a bird nest in quick succession.