The normal pregnancy takes about 40 weeks, which gives us enough time to prepare for the little one's arrival. The things you need to prepare may depend on your culture background, where you live, your personal circumstance and etc. However, its always a good start to have a chat with nearby vetaran mums asking them what are the most essential things, what nappy brand is good, where to shop and etc. Nowadays, you can join mum's communities online, e.g. Nct.org.uk. You can also get helpful advice from your midwife.
Departments (e.g. John Lewis) usually have nursery advisors where you can non-biased advise. Basically, you need to prepare things in the following six categories:

1. Sleeping
2. Bathing & Changing
3. Feeding
4. Travel
5. Clothing
6. Play

You can find items suggested for each category here. You do not need to buy everything new although things like Mattress and car seat are advised to buy a new one for each baby. Always do a price comparison online to find the best deal.