use a good quality sewing thread in your bobbin and all above ...also, you really have to slow down! the thread stretches and breaks if you are sewing fast...you have to slow way down in order to get anywhere. personally I HATE USING INVISIBLE THREAD! it is expensive a pain to work with, melts if you hit it with an iron...after a few years of quilt washings it starts breaking, then you get those lovely picky points ... like that tag in your favorite t-shirt that pokes the back of your neck and drives you nuts till you remove it.
i know there are people who use it all the time, love it and have no problems...i really admire them...for me...not so good...