You will remove your needle -plate, bobbin, and bobbin case and clean that area out entirely of any excess thread, lint, or debris. You can do this with your brush or use a tweezer. Next, place a drop of sewing machine oil in the center of your shuttle (metal piece holding bobbin and bobbin case).
Reassemble your bobbin area.
Unthread your machine and raise your presser foot to open your tension discs.
Take a scrap piece of material and run it through your top tension back and forth in the pathway of the threading. Cleaning will remove any lint, debris, or extra thread you have that does not allow your top tension to close correctly.
Now rethread the machine, making sure you correctly take up the lever and top tension through your guides. Before you go through your needle, keep gently pulling your thread while lowering your foot. You should feel the top tension beginning to grab your thread. If not, you are in front of or behind your tension discs, so rethread it again.
If that does not work, there may be a thread around the take-up area. Next, remove the faceplate (cover on the upper left end of the machine).
Inside there, you will see the connecting mechanism for the thread take-up. There will probably be a thread wrapped around that to remove the mechanism and lubricate it.