Any advice for first time renting of a car?

I am 24, first time renting a car for a 5 hour drive to a good friend's wedding. I have reserved one online with Hertz using my AAA discount, it looks like for 4 days it will cost me $109. However, it doesnt say how much it will be with my age of 24. I am a safe driver, but I am curious as to what it may jump to. Also, any advice in general for the experience of renting a car? I figure its best to be prepared.