if your tension is *off* you need to adjust it...many of the new machines are pretty good at adjusting their own tension...you don't mention what your machine is??? your user manual should te ll you exactly how to adjust your tension-and when it is necessary- or maybe you could take a *sewing machine owners class* at a local dealer to learn exactly how to use your machine- that would help you understand all the bells & whistles, maintenance, and trouble shooting. back in the 60's not only did they not generally touch the tension...but they also prided themselves in using the same needle for 20+ years!
things have changed with time- now we have tons of choices in threads, stitches, fabrics, needles, techniques, it's all different now. if you do not have an available class and you want to learn about tensions take some scrap fabric pieces (folded in half-or 2 pieces) get out your book & start doing some adjusting---stitch a line- straight stitch & zigzag and look at it---then adjust some more---use contrasting thread that will show up well---just do some experimenting...but pay attention to what you are doing- and write down what is *perfect*... but remember- different fabrics, threads and stitches sometimes need a bit of adjusting...it's nothing to be afraid of- just get comfortable with your machine.