Regarding the title of this post: don’t do it.
In fact, I can’t caution you against it strongly enough. Instead of trying to make your own wedding dress, or your prom dress, just go to a site like DressFirst and pick out something nice, click the purchase button, and wait for the UPS man to show up with the package. It’ll save you a lot of heartache in the end.
The problem isn’t that you don’t have excellent tailoring skills, it’s that unless you’re a professional seamstress and/or dress designer, making fancy evening wear is a very specialized skill, one in which minor mistakes can quickly spiral out of control and turn into world-class disasters. And because the typical fabric used in constructing homecoming dresses and prom dresses and bridesmaid dress is so expensive, a simple slip of the scissors or the sewing machine can cost you a bundle.
When you move into formal wear, you’re moving into very dangerous territory. The jungles of Africa have nothing on it.
If, however, you choose to ignore my warnings and do want to start making evening wear, use yourself as the guinea pig first. Wear your own clothes until you get good enough to make things for others. The last thing you want is to promise to make someone a prom dress (for example) only to find that you’re not able to complete the dress in time for the big event, or that your skill set wasn’t up to the task of producing something that’s supposed to be elegant and well-finished.
So, to recap. Want to make evening wear? Don’t do it.