Here are some thoughts from a some-time sewing teacher, whose mom was a sewing teacher before going back to school. Despite trying on me starting at age 6, and being in her sewing classes in junior high, she didn't manage to teach me anything (my classmates still rave 50 years later about learning from her!) The two daughters who became sewing fanatics didn't get into it until our 30s.
Starting with what you want to make is a great way to learn (rather than the classic approach of 'learning to sew via a series of less-simple projects). It can be much more motivating. Remember that people learn differently and if one explanation fir anything doesn't make sense, go find another in books or on the internet.
Machine tips: Once it's working reasonably well, remember that almost all bobbin messes (also known as nesting, when things stop because of a lot of bobbin thread looping up) happen because the bobbin is in the case wrong. Bobbin thread can unwind clockwise (q) or counter clockwise (p), depending on the machine; if you put the bobbin in the case upside down it will go the wrong way.
The other contributing factor to lots of problems: not using a fresh needle. Some advise changing needles at the start of each project. I change at lease every time I put in a full bobbin (you've stopped anyway, and maybe unthreaded the needle to wind a bobbin --good idea to wind a couple of them when you're doing it). Needles are different sizes, too; larger for thick fabrics, smaller for thin. Ball end for knits. You can use the threader in sewing kits if your machine doesn't have one.
Needles are the cheapest way to good sewing; others that make an enormous difference are light bulbs and irons. Put the brightest light bulb you can in the overhead lights; compact fluorescents have made it possible to put a much, much brighter bulb into fixtures with incandescent limits. A really bright one (maybe for photography) can cost a few bucks more than normal ones; you'd be surprised how many folks with multi-thousand dollar machines can't bring themselves to spend ten bucks for a light bulb.
Irons: same with irons. You can't spend too much attention to pressing, and if your iron is more than a couple of years old you will be stunned what $20 or $25 can get, iron-wise. Put it as close to the machine as possible, every step away is a seam that may go unpressed.
Presser feet: will save you more time and effort than you can imagine. It's almost always worth a couple of minutes to change to a specialized foot (but not rare or expensive), like the ones for narrow hemming, gathering and binding, no matter how small it looks like the job. Also, many sewers are suddenly addicted when they operate a ruffler attachment for the first time.
Two mistakes in a row concerning the same/similar things are probably related. Ie, if the first is wrong it makes the second wrong too. Two blips (needle unthreading, stabbing yourself, many others) in a row means you need to take a break, have some tea and aim your eyes somewhere else. I had a friend in college, probably the best sewer I have ever met even then, who was making 12 gold lame jump suits for a dance class. She discovered late at night she'd attached legs to necks, and somehow put three arms on one. Relatively recently I serged myself to the machine! (I was wearing a shirt the same color and very similar fabric to whatever I was trying to finish at three a.m ) The lesson: you'll make mistakes and they're a lot easier to fix the next day.