The sky’s the limit when it comes to style. I encourage bringing 4 or more outfits to your session. We may not use them all, but it’s great to have a variety of styles to choose from. Simple, timeless outfits are best. I usually recommend avoiding outfits with writing or logos (unless they are part of your aesthetic or sports/school logo), the images should be all about you now what brand you're wearing. Fine lines or pinstripes are not recommended, they tend to be hard to print and look odd in digital images. 
Props! I highly recommend bringing props to your senior session. Music, books, sports, dance, art, hiking, horseback riding, skateboarding, your car, your pet, etc. anything that you love and what makes you unique will be a great addition to your portraits. Talk to me about customizing your session to include some of your favorite things!
Above all, be yourself! Make sure what you wear makes you comfortable and reflects your personal style and taste.