1. Content - first, not last
The importance of content, and the effort required to create it, is nearly always underestimated. We suggest you start thinking about the content your users will need and who will provide it as early as you can. Plan for it, resource it properly, and leave plenty of time to create it.
2. Code - does it work on everything?
These days your site should work on any device and in any browser. (OK, maybe not IE6 but that's another story). Some would say think mobile first. At the very least make sure your agency creates code that is clean, accessible and Web Standards compliant. If it isn't you're storing up trouble for the future.
3. User research - allow enough time for discovery
What your users will tell you, if you take the time to ask, will probably surprise and enlighten you. Allow their insight to influence your direction. Make use of their ideas to deliver a better, more usable and useful product. They'll thank you and respect you for it.
4. Planning & strategy - taking the bull by the horns
Now is great time to re-conceive your business in digital terms. How would you design your business if you were starting from scratch? What services can you deliver online? What new ways can build trust and loyalty? What efficiencies can you gain by giving people the best digital tools?
5. Content again - set it free
You know your audience. You know what they're into and what they want from you. You know where they congregate online. Now you need to push your content out so that they can discover and share it. Don't store it up for a brochure or annual report - if it's good stuff set it free.