The highly flexible nature of the internet means that websites appear and disappear every day. Thanks to Donald MacLean for reminding me that another currently popular university-managed site containing useful resources for prospective PhD students is http://cloudworks.ac.uk/
This is a freely-available, open-access site, although you will need to register to obtain access. Once you have entered the site, search for “PhD” to find a link to “research skills required by PhD students”. The supporting text has short articles on a wide range of issues such as what is meant by ‘critical thinking’, how to select and justify your research methods, and tips on how to organise and present your work so that other people can appreciate your work.
Like all of these sites, this one will not answer all of your questions, but it does contain different perspectives and useful information from people who have a lot of experience. When you are just starting out on your PhD research, not all of this advice will seem equally relevant. It makes good sense, however, to familiarise yourself with the variety of information on the site, and bookmark the URL, because you might want to return to these topics later in your studies as these issues take on a new relevance. This advice also applies to the supervisor, because you might wish to direct your student to read the advice which will reinforce (or give a different perspective to) guidance that you give to students in tutorial sessions.