There are many ways of choosing a supervisor. You may wish to continue working with someone who has taught you before. You may have developed a research interest at undergraduate or more probably at MA level in a particular topic, and know their work, or have been referred to them as academics in your field. They may be attached to the institution at which you have decided to study or to which you have won a grant, or have been selected by a head of department as the most likely to correspond to your specialism.
Factors to take into account
Yet, it can be risky to chose a supervisor that you don’t know well already – this is not to preclude it, but simply to make you aware of the potential pitfalls. Perhaps the most common cited problem (and problems do arise!) is that PhD students feel they don’t get the sustained and continuous support necessary for them to complete their research degree to the proper standard, or that it came too late for them to do anything about it, or that the supervisor didn’t have enough time for them.
The most important thing of all therefore when choosing a supervisor (and it is often your choice) is to check that they have enough time to take you on. Having a PhD student means not only getting them to PhD standard, but also providing continued support in the often arduous job market, as well as writing numerous job references. All this can be very time-consuming for an already over-stretched academic, and with the best will in the world, clever, nice, charismatic (whatever!) as they are, they may not be the best person to go for. This particularly applies to celebrity academics or to those who may not be actively famous but have written 20 books all of which have an excellent reputation. Ask yourself whether the person who teaches and still finds time to write 20 books or do t.v. programmes, etc, can possibly fit you in. That is not to say that they won’t, but just to tell you not to be starry-eyed about the most glamorous people and to warn you to be realistic about what you need. If you know that you like a lot of hands-on support, make sure you chose someone who can provide that. If on the contrary, you find that the occasional acerbic analysis of your work gives you sufficient stimulus, then the person who’s written 20 books and can give you a quick 45 minutes every other month may be the person for you. While many institutions lay down guidelines for the amount of supervision a student should expect to receive, not everybody follows them to the letter - nor would strict obedience be desirable in the eyes of all supervisors or indeed all research students.
It is important to be clear what you want, or need, from a supervisor. They may be a great expert on the precise field in which you want to work (a particular author, say). Or they may be exponents of a theory or method that you want to work with, in a different field from theirs. Or they may be neither, but have a general knowledge of the broad field, and of different approaches to its study, and sufficient pedagogical skill and experience to be able to direct you effectively. A supervisor of any of these types may be very successful; but try to get clear in advance what it is they can offer you. If you are working, for instance, in an area where very precise skills or knowledges are required (e.g. some kinds of bibliography, or history of ideas, or advanced psychoanalytic theory) you may need the specialist, not the generalist.