If you tension is OK when sewing, then don't mess with your tension. Is your thread shredding and breaking with normal sewing or only FMQ? Usually thread breakage is thread hang up above your needle or your needle is not matched with your thread weight. FMQ requires a large eye needle. Also try 50 weight thread or above that. There are some quilters using 90 and 100 weight thread. I use that for machine applique. Check all along your thread path, from your spool to the guides, tug and see if you have a "hang up" as you go along your thread path. I was at a FMQ Boot Camp a few years ago. They told us to bring a 90/14 microtex needle. I put it in my machine, I got out my brand new thread spool, and my thread started shredding and then the needle broke....hit my glasses. The instructor looked at my machine and needle....she couldn't see the problem either. I looked at the thread spool (small cone from Superior) and inside the end of the cone it said what needle to use. I purchased it from the shop where the class was and I was off and FMQ.....learned a valuable lesson that day. Match your needle to your thread. Of course, you would match a needle size to denim and leather use. In this case the Microtex needle worked for everyone except my thread. The Mictrotex needle has a sharp point, so less drag on the fabric. Practice with new needles and 50 weight thread or higher and see if that helps. Best wishes in getting the FMQ and ruler use tackled.....just takes practice.