First simple fix would be to change the needle for a fresh sharp one, the right size for the fabric you are sewing. Blunt or burred needles will cause poor stitching, missed stitches and often a popping or squeaking sound. New needle for every 4-6 sewing hours is the rule of thumb. I put in a new one for each new project and that way, I know it is fresh and the appropriate size and type. Use ball point needles for stretch fabrics and regular needles for woven fabrics.
I can not see a threading diagram for your machine on line but this site http://sewing.about.com/od/sewingmachineindex/ht/threadmachineht.htm
has good step by step instructions and also photos identifying the important parts of a sewing machine. They vary between makes and models but once you understand what each part does and how the stitch is formed, it is straightforward to thread up an unknown machine as they always have a similar path from the spool, to tension device, to a take up lever, then to the needle. Same applies to the bobbin, whether it is top loading or horizontal. There is a right way to put in the bobbin, and always some sort of tension spring or device which controls the release of the thread from the bobbin during stitching.
I can not find a 393 image either but here goes on the above image. Put the thread onto the spool pin on the back of the machine, right hand side. Sometimes the pins are retractable and need to be pulled up, others are fixed in place. Take the thread tail from right across to the left side and around the thread guide on top of the machine, the little metal hook, then down the front of the machine on the right hand side of that long dark green panel, at bottom, reverse direction and take back up the left hand side and catch thread into the take up lever. You can't see it in this photo, turn the fly wheel towards you until it raises up to its highest point and thread or pull the thread into its open end. Now back downwards towards the needle. There is usually a thread guide on the needle bar, hook thread behind this, then thread the needle and pull a tail of about 10 cms out under the pressure foot and to the back.
Now thread the bobbin, clicking the thread tail into tension spring. On many Janomes, the bobbin cover is a clear plastic piece and has an image showing the right rotation for the bobbin to make things easy.
Now turn the flywheel towards you holding the top thread tail firmly, go through one downwards movement with the needle, then back upwards again and pull the thread tail, catching and pulling the bobbin thread up to the top of the needle plate. Both threads under the foot and out the back and your ready to sew!