I'm so excited for you!
I would suggest clothing that is light and loose, i.e. cotton blouses/tops, skirts, cardigan, trousers, and a scarf or hat to protect your head from the sun. Personally, I prefer to wear long sleeves, but many tourists wear short and 3/4 sleeves. Be sure to wear shoes, not sandals as the sand drifts everywhere and the streets can be a bit mucky :)
What not to wear: skimpy t's, short/tight/revealing clothing that calls attention to the shape of your body.
Although I didn't go to any nightclubs while I was there, apparently the dress code is much more relaxed and westernized, same for the hotel and resort areas frequented by tourists.
Here are some excellent suggestions by Keti Sharif:
Keti's Travel Tips for Egypt
Happy planning!
Khalida