T-shirts, jerseys, track pants and football shorts are good workout clothes for guys. Check if you can do lunges and side lunges to make sure your pants are not too tight. Don't wear oversized shorts. Consider the material as well, don't work out in something that's likely to tear if stretched. It's convenient when you don't have to keep pulling up your pants after every set – wear something with an elastic waistband. I personally don't like wearing black because then I can't see the sweat. Sweat serves as a visual reminder of how hard I pushed myself with the day's workout. For girls, wear yoga pants and a sports bra. If you're going to the gym then wear a big T-shirt on top. If you're doing deadlifts then you might want to wear thick tennis socks.
Keep a few sets of these clothes available at home.