good thorough cleaning- new needle- rewind bobbin- rethread (from spool all the way to needle-
this can be caused by many different things- but usually winds up being a piece of lint somewhere- a dull needle- or not threaded quite right...so those are the places to give attention to first- if after all those things are done you still have a problem - it may need to go to a shop for a check up=adjustment--all of the above should be done before doing anything with the tension.
also- make sure you remember to drop the foot- sometimes we get ahead of ourselves- and forget that- that can also cause the same mess