Not sure where I picked this little gem up from but it's so true. Most sewing machine issues can be solved by giving these three things a quick try.
If this doesn't work then:
- Make sure the area under the plate is clear of lint using a cotton bud and small brush.
- Change the brand of thread/needle you're using - I highly recommend sticking to Gutermann and Prym here as these are high quality brands and I've never heard of a sewing machine that didn't love them!
- Run a few straight and zigzag lines through a scrap of fabric, look at what's going wrong, then google it! Youtube and blogs have some fantastic tips and tricks.