First let me thank you for your kind words about my website.
I'd say experience gives you the most confidence. When I first started this business, I was given a pair of jeans that needed a new zipper. I let those things hang there for 2 WEEKS! I didn't know how to start and was petrified of making a mistake. Finally I dove in. Looking back, I should have practiced on an old pair first. But I finally put in the new zipper. It only took me about 2 hours, because I made so many mistakes that I had to rip out!!! Now it takes 20-25 minutes.
So practice on some old clothes first. It will give you a pat on the back to know you've done it. Then the next thing that will improve will be your speed. The more times you do things, the quicker you will finish them. Then your hourly wage will go up because you can do more in one hour than you did last week. I still work at this, even today.
I am putting up the "Shorten Suit Sleeves" page this week, so you may feel more comfortable waiting for that. When you work on something like that, you have 2 sleeves, so look at one while you work on the other. I try not to rip out both at the same time.
Also, use a digital camera. Snap shots of things you do, step by step so you have a record of how to put things back the way you found them.
Good luck and let me know when you get stuck. I'll walk you through it.