Whether you're planning on tackling a church website on your own or with a slew of volunteers, here's a book that should help: A Simplified Guide to Church Websites: Purpose, Planning, and Presentation. The book gives arguments for having a site and updating a site, but it focuses even more on the elements necessary to create an effective church website.
About half of the book is dedicated to real-life tips and tricks you can use to make sure your church website looks and works the way you want. It gives a rating scale for how important and difficult certain elements are to implement. There are plenty of photos to help you see the parts of the site you'll want to design, but it also works as background knowledge for when you decide to hire someone else. Will that web designer add a favicon or a copyright year that stays current? Will you have to pay extra to play videos? How should pictures be handled? It's all in the book.