Here's the basic tools I've found very useful:
1. seam ripper. Don't start without it, this is what a long time sewer told me to get when I started, and she was right.
I like the one with the sort of curved blades end, with the little plastic ball on one of the tips, all these things will make sense to you the more you use it.
2. A magnifier, this really helps to see what the stitches are doing, if the tension is too high or too low. I use one of these jeweler's magnifiers, the little cones, they are about right.
3. Good light.
4. Delicate thin fabrics are going to be a challenge, use very small needles, 9 or 10 size. Silnylon is really hard to sew, so if you can sew that, you can probably sew most of the other fabrics.
5. Extra bobbins, so you don't have to wind the bobbin for every new thread color.
6. For light fabrics, a straight stitch presser foot, this is really helpful to get rid of those annoying puckers that the zig zag foot makes more likely. Tip: you can zig zag a little bit with the straight presser foot as long as the needles don't hit the sides of the hole. Other nifty presser feet you can get too are things like flat felling ones, hemming ones. Haven't tried those yet, but will.
7. Sew slowly, on the lighter fabrics. That helps to keep them under control and feeding consistently.
If you have tried everything and the machine just won't sew things right, consider borrowing another machine from someone and try that one, I saw a really big difference between my first one and another one I picked up, one can barely sew silnylon without the seams slipping and the fabric slipping, a newer one that is cheap light weight pfaff hobby 307 can sew that light stuff fine as far as I can tell. So if you've given it a few weeks and you just can't get the machine to do consistent stitches the problem may not be you. My old machine has a regular speed pedal thing, the pfaff has an electronic one, and it's much easier to maintain slow speeds with the pfaff.
Get seconds of silnylon, they don't cost much, questoutfitters.com has them, so do some other sites. Some have suggested finding silnylon in Walmart, but I can't bring myself to go to that store so I'm not recommending that.