Semi self taught, along with learning from when others have helped me.

Have some bought patterns, if you keep an eye on spotlight or lincraft, they often have deals. Otherwise they can be exxie. If you pick right and find a pattern that has some good variations, it can last you awhile. Also I don't cut along the size lines of the patterns, I do my best to trace the pattern onto the fabric following the size line I want. That way I can use the full range of sizes for the girls.
I was taught by my mum to cut the pattern to the largest size and then fold to the smaller size where needed and to trace the bits you couldn't fold (ie if it was a round curve) onto another piece of paper and just use that piece for that section. Not sure if Ive explained it right, but its easy and simple to do.