#1: Add some lipgloss or lipstick (NOT chapstick!). A pretty pout will not only make you look together, but will give you something to smile about. And let's be serious, a smile is your best accessory anyway! :}
#2: Curl those lashes. As awkward as I used to find this task, I have come to realize how magical it actually is. Trust me, if you don't already do this, try it! It takes a little while to get used to it, but it will be worth it. I really love this trick -- it's quick, easy, and it's so effective that I use it often to replace mascara.
#3: Put your hair in a half-up 'do. This is my go-to...for reasons I cannot explain, nine times out of ten a half-do makes my hair look good when only moments before my bedhead-disaster was threatening to ruin my day. Seriously. A half-do.
#4: Throw on some bracelets. I have a casual go-to set (that includes a dressier ponytail holder...just in case!) I always reach for to make my outfit look like I planned it. I really think it adds a nice touch, even to a t-shirt.
#5: And of course, the obvious...add some awesome shoes. Whether it's glitzy sandals, boyish loafers, your favorite boots, or killer heels, the right shoes can transform an outfit. And no one will think you got ready in the dark.