Getting my hair dyed for the first time?

On my fourteenth birthday I'm planning to get my hair dyed at a salon. I am a brunette naturally, somewhere between a very dark shade of brown and black, but I am planning on going blonde. Not bleached or baby or anything because my skin is pretty pale and I don't think that would suit, but "medium natural blonde". This will be the first time I've ever had my hair dyed so I was just wondering if there is anything I should know, or if you have advice on how to care for it or anything? Also I wanted to check, I know it will take my hair some time to grow back completely and all, but when it does will its natural shade be affected? I'm thinking semi-permanent at least because it's the first time, if that helps. So thanks for taking the time to read and thanks in advance for the answers=)