It's horrible for your hair to wash it every day. It dries it out, causes it to overcompensate by producing too much oil, breaks it, and you end up with damaged, frizzy, oily, dry hair. NOT the look we're going for.
I admit, I fell into washing my hair everyday because I didn't want to deal with oily/greasy looking hair. I've been very strict with washing my hair every other day though. When I jump into the shower, if I'm not washing my hair, I clip it up high so it doesn't get wet. You can even throw a shower cap over your clipped up hair to keep the steam from making it greasy looking.
On days I don't shampoo, if my hair looks like it needs a little bit of help, I use dry shampoo. I picked up this Tresemme one from Target for oily, straight hair. The directions say to shake vigorously, spray it in, wait 1-2 minutes, and brush it out.
Personally, I'm not pleased with this dry shampoo. I'm inserting a picture of my hair, post dry shampoo, below.