My advice is to go in for it and not be so very afraid, but at the same time be very clear on that you won't do anything you're not comfortable with and that you always make sure that what ever your Master tells you to do, you're comfortable with. Make him in advance realise that he has to respect when you need a break from the lifestyle.

Being a new slave means that you'll probably have a lot of feelings of shame and confusion at first. These feelings should not be ignored. You need to address them and deal with them. Preferably with your Master. The worst thing that can happen is a slave just going in for being 100% submission and then all the repressed emotions make her run away. Open and clear comunication is the key. If the Master isn't willing to listen, then get the fuck out. Atentiveness is the one most important charecteristic in a Master. If he's sensetive and smart enough you won't even need safe words.