I'm on the e-mail list for Craftsy, a website that has a number of online sewing courses. They have a course called "Tailoring Ready-To-Wear" and I have considered signing up for it so I can learn how to do a better job of altering my own clothes. I haven't done it yet so I can't speak to the quality of the course. A friend of mine did one of their other courses and made a really nice vintage style suit jacket. They do have sales on their courses a few times a year and I think I might sign up during one of those.
I'm also a longtime follower and fan of the Refashionista blog but to me she's more about taking a garment and making it into something completely new vs. making a few tweaks to change an ill-fitting garment into one that fits perfectly.