On the contrary to what a lot of posts here say, I'd say read baby books, but make sure you read more than one, and preferably with opposing views as there is no one right way to do things. Many people say 'trust your instincts' - well I for one had no instincts and no experience with babies, don't worry if this applies to you too - read books and talk to other parents, then pick the bits of the advice you want to use.
Smile and nod benignly when your MIL (or anyone else for that matter) offers advice, then ignore it and do what you think is best. Mine told me I should leave DD1 to cry to 'exercise her lungs' - complete twaddle (although DD1's lungs did get a lot of exercise and she's now a cornet player, so maybe it worked).
Get out, go for walks, go to parent and toddler groups (you can normally go with a newborn, so don't worry that you don't have a 'toddler'), meet friends if you can. Not in the initial days of course, but you'll soon be driven mad if you stay at home the whole time, especially if your baby is a cryer. A baby is a wonderful ice-breaker if you're shy about going to places for the first time on your own.
Sleep deprivation is used by some regimes as a form of torture, so don't underestimate how hard it can be. If someone offers to take your baby for a while for you to have a sleep, don't turn them down. They all sleep eventually.
Don't be afraid to get help if you think you're suffering from post-natal depression.
Don't worry if the birth doesn't go quite according to your birth plan - it makes no difference in the long run, the baby's out, and that's all that matters.
Good luck, I'm sure you'll be fine.