Getting familiar with fabric is really important before you get into sewing. The right fabric can make a garment, or break it if its the wrong weight and drape. Some of the biggest sewing fails comes from pairing the wrong fabric with a pattern, not necessarily from poor technique or sewing quality. So you should become familiar with the difference between knits and woven (remember, knits are stretchy like t-shirts, woven for the most part are not), as well as some of the different types of each. For example, a lightweight jersey knit is going to drape and sit completely different than a heavier weight ponte knit. So pay attention to what a pattern suggests for fabric.
If you're able to go to a fabric store in person and touch and feel the different kinds of fabrics, its a quick way to learn. Otherwise, some online fabric shops offer swatches for a few dollars each so you can feel for yourself before committing to a lot of yardage.
Speaking of online fabric shopping, these are some of my favorites! I know there more out there, so if you have another go-to, don't forget to tell me in a comment below!:
Another note on fabric - when building a handmade wardrobe, you'll want to keep in mind your personal style. You want your handmade pieces to fit flawlessly into your closet/wardrobe. It can be easy, when fabric shopping, to get sucked into really fun and flashy prints or other fabrics. But stop and think if it really fits in with the rest of your wardrobe. Maybe that is your style - colorful and lots of prints! Hey, thats cool! But does your wardrobe contain mostly muted solid colors? Or just subtle florals? Is that bright yellow cat print really going to work with your other garments, or do you only attracted to the fabric because its cute and stands out? Just keep it in mind! I still struggle with this every time I buy fabric. I'm drawn to those quirky fabrics, even though its not actually my personal style anymore.