So, after you take the plunge and pick out a sewing machine, what do you do? The rational answer is to take a class. Many times, the store that sold the machine will offer a free class and you should probably take them up on it. Or you could have an experienced friend give you some lessons.
I didn't do either of those things, because I'm incredibly impatient and stubborn. I like to learn by jumping in, so I thought of some projects I'd like to do, purchased a book, read some online tutorials and got started. This works well if you're hands on and learn by troubleshooting. Have the machine manual close by at all times because you'll be referencing it constantly while you learn how to wind a bobbin, thread the machine and change the feet.
Book resources - I purchased a copy of Bend the Rules Sewing by Amy Karol, and read through it before starting anything. It is very basic, which I prefer because it doesn't feel as overwhelming. I never did end up using many of the patterns, but reading through the instructions for each one gives you a feel for how to design your own simple projects.
Online resources - There are so many amazing online resources that it's hard to narrow it down. If you're ever trying to figure out how to do something, just search for "xyz tutorial" and start scrolling. Amy Karol has a blog and does great video tutorials as well. I love reading Freshly Picked and her tutorials are incredibly easy to understand. Sew Mama Sew has tons of tutorials and forums as well.
First projects - I wouldn't recommend starting with clothes. They use up a lot of fabric and you're likely to mess up at first. Aim for projects that use mostly straight lines and then move up. I made a lot of placemats in the beginning, using old sheets that I had found at the thrift store. This is a great way to get used to the feel of the machine without much pressure.
After the placemats, I moved up to small bags, a larger bag, an apron, a pillow case, a bathmat, and then finally tried out clothing with this top and this skirt (the skirt is actually so easy that I could have done it earlier).
And a little last word of advice - sewing will be frustrating sometimes. That's okay. The satisfied feeling you get when you complete a project is worth it, I promise. Find a little block of free time, make your space nice, pour yourself a glass of wine and start working. If you feel yourself getting fed up, take a break. It's usually easier when you come back to it.