I have naturally v. dark brown hair and was blonde blonde blonde for a number of years in my 20s. NEVER wash your hair every day, even when it's not colored -- it is bad for it! With undyed hair try every other day, but with a serious bleach job, you should only wash it with shampoo every two or three days at most -- go longer if you can and it's not really dirty. HOWEVER, get it wet in the shower every day and get a really good leave-in conditioner. I still use Paul Mitchell's The Conditioner every day even though I am back to my natural color. Just put a dab in your hand after you turn the water off, pull it through your hair making sure you get the ends really well, and either then comb it through or just wrap your head in a towel for a bit. It won't make your hair perfect but it will help with the dryness. You should also be sure to get the ends trimmed regularly -- in fact if you can go a couple inches shorter now since you've just bleached it that will help a lot.
To redye it back you need to wait a couple of weeks, but hey, it's fun to be blonde in the summer! Play with it a little and then dye it darker in the fall. A bonus: adding color back in will make your hair feel super-soft at first so that is something to look forward to.
One more bit of advice: Always get a pro to bleach your hair from very dark to very blonde, unless you're a kid and don't need to worry about doing some damage.
Enjoy your summer blonde!