I had my mom sit down with me for a few minutes with a sewing machine, and then I started with flannel pj pants. I don't pre-wash fabric for quilts, but I do for clothing. You don't want it to shrink weird on you. For flannel, I usually wash it and dry it twice to make sure it's done shrinking.
The pj pants were good because I could learn some basics (sewing straight lines, curves, using the button hole attachment, sewing elastic). I learned how to play with the pattern a little (make the legs longer, the waist shorter). And, even if I didn't do a great job and made mistakes, they were still usable since I don't plan to wear them in public.
Next project was a shirt. I can wear that one in public :) If it's stretchy fabric, use a "stretch needle" and a zig-zag stitch, so that it can stretch with the fabric when needed (collars, sleeves...)
And then an apron-- more curves, learning how to gather the fabric, things like that.
Now I'm making a vest for my son. Yes, he could go out and buy one, but they aren't cheap, I never see them second hand around here, and he got to pick his own colors (grey vest, deep red lining). To test the pattern, I've only cut the lining so that he can try that on. The fabric was less expensive, so if it's too small, I didn't waste the more expensive fabric (and, in the end, I still wouldn't waste it as I could use it for other projects, pockets, etc).
I'm also just starting, but those are things I've done. If you have a JoAnn Fabrics in your area, sign up for their emails and also get them online. They almost always have sales/coupons, so I only pay full price for anything if I absolutely have to.