Before contacting a web design agency, it's best to think about what you wish to achieve. In one sentence try to summarise what you need a new website for, and what you want the website to achieve. Set some goals and aims for the project and think about how you will measure the success of the website.
Your current website analytics may help you see where traffic is coming from, and which keywords users are using. For example, this website is commonly found by users searching "surrey web design agency" or "surrey web development".
Content is essential, there's no way around it. Even if you're just a photographer - content is important for search engines. Think about how you want your website structured, and the possibility of landing pages. Landing pages are well suited to advertising as you can target key audiences.
Most websites will last 2 to 3 years, so it's worth investing money in your website. If you're budget is low, try to think about how your website could be built in stages. Along with the cost of the website, you'll need to consider your time to write content and liaise with the web developer.
Another cost that is often forgotten is website hosting. The last thing you want is your server or website to be hacked. Larger companies could use a dedicated server, smaller companies could use a shared hosting solution.
Finally, think about backups. Your website should be backed up by a third party service. This ensures that your website can be recovered if the server goes offline. Hard drive failures are not uncommon, and can happen at any moment. If the website is business critical, you may want to think about a hot backup server
Purchasing a domain is really important, and something you may wish to bear in mind when choosing a company name. Your domain name needs to be easy to find, easy to remember and easy to spell. Consider the "tld", top-level domain, as this may or may not be available in your country. ".co.uk" or ".com" are common, but you could also purchase ".uk" or ".co".