Domains are a key part of the Internet, allowing people to enter a single, easily memorable string of characters (such as google.com) into their browser to reach a resource, rather than a seemingly arcane string of numbers. Domains in higher education tend to end with the .ac.uk. characters, a subset of the domain space which is managed by JANET. Each institution will generally have one root domain, such as lincoln.ac.uk, within which they can create and manage their own subdomains to allow people to connect to individual services.
Whilst Linking You focusses mostly on the identifiers which are part of a domain (predominantly within the root of the domain), it's worth looking at a few best practices and suggestions for keeping the domain space clean and easily understood.
Everybody is used to seeing the letters www. at the start of a web address, but they're not actually a requirement. Their presence is historical, stemming from when it was necessary to prompt users to enter the domain in their web browser, implying that the website was part of the "World Wide Web". Since users are now much more familiar with the process of visiting websites, any use of the www. prefix can be considered redundant.
Linking You recommends that websites at least support accessing them without the www. prefix. You can find arguments for this approach, as well as necessary code snippets, at the no-www campaign. The transition to supporting a domain both with and without the prefix is technically very simple, and does not require any significant amount of work.
Making the www. optional has many benefits, including faster reading of the web address (it has ten fewer syllables), requiring less space on printed or advertising material, removing redundancy and making the address easier to type (in the case of short root domains such as ox.ac.uk adding the www. makes the address a whole 50% longer).
Avoid Mystery Subdomains
It may be tempting to create subdomains with long-winded descriptions, internal acronyms, codenames or similar. This should be avoided wherever possible. If you've got a service which allows people to top up their printing credit try to give it a domain such as print. or topup., rather than topupmyprintaccount. or onlinemoneyloader. The shorter domains are far easier to remember, and much more intuitive.