If I could sit down every single new sewist who wants to learn and improve their skills I would tell them the following things
Read the manual. Work through the manual from front to back. Read the troubleshooting section even when you're not having a problem. Read it. Keep it handy. Maybe download a PDF too, just in case the hard copy walks off.
Buy an iron and ironing board. They don't have to be fancy, a bigger board is only better if it is stable. An regular Ikea board has worked for me for years. A $20 iron from Walmart will noticeably improve your work. Press every seam before another seam intersects it. Don't just iron at the end.
Sewing machine needles have sizes AND types and you need to match them to your fabric. They also wear down. The often quoted rule is 8 hours of run time and its a pretty good rule.
The problem is almost never the tension settings, and even less often is it the bobbin tension. The problem is almost always your threading or needle.
Clean your machine. Do not use canned air. Take off the plate under the foot and use a brush and or a keyboard vacuum to get the fluff out.
