my first day was so bad i nearly quit right then and there. i guess that was a bit of a special case though.
considering my experience the advice i'd give is simply: just in case things go wrong, have a phone number or an office number of someone with you so you can go talk to someone if you do suddenly find you need help (or someone you can cry on). in most cases this will not be necessary - it's just a safety net.
good luck! most probably it will be fun and exciting!