Skipped stitches can be very frustrating. You need to make sure your needle is new and is the correct type and size for your thread and project. Re-threading the machine both top and bobbin is many times the answer. Cleaning and oiling are mandatory. But after all this is said and done many times you are still having an issue.
I have made this video to show you how important the height of the foot in relation to the surface of the fabric can be. If there is too much room between the bottom of the foot and the fabric, you can get flagging which will cause skipped stitches. Flagging is where the fabric has room to move up and down with the needle.
I hope you enjoy the demonstration and it helps you to solve a skipped stitch mystery someday.