Well, straight hair isn't always the easiest to get curly (my hair is wavy, but hold a ringlet? Never).
What I like to do is this. I get out of the shower and then i towel dry my hair. Really important, DON'T COMB IT.
Then, I rub a little Garnier Sleek and Shine through there, and then I use something called Surf Hair, which is also by Garnier. It's REALLY sticky, so you just want to use a little bit of it. I just spread it pretty evenly over my palms and the scrunch my hair from the tips to the roots. Just scrunch a handful of it and hold it to your scalp for awhile.
After that, I use some of the John Frieda Blonde Tousled Tresses spray...(I think they make a brunette and a redhead spray as well) and do the same thing again, scrunching from the tips to the roots. (Don't use a lot, otherwise it'll look greasy.)
And then just let your hair air dry. The curls will be very wavy, and your hair won't be crunchy from heavy hair spray.