The new sewing machine I bought last year has got me back into thread tension territory. It is very particular. My other sewing machine was never a problem like that. Thread tension can be affected by a number of things and when the machine is sewing loosely or puckering the material it is really annoying! My new sewing machine likes the right needle. It likes a sharp needle. It doesn't like any dust or fluff in the bobbin case. It likes a full bobbin and prefers plastic bobbins to metal ones. After a year of sewing with it I now have a checklist! It's a great machine and can manage so many things more easily than my other one. Every machine has its character and foibles. There are some good ideas to help on the threads magazine site. The video runs you through the basics.