There is lots of advice on the CILIP website about how to choose a mentor, however here are my tips for things to consider:
Look and see if there are any names that you recognise - these could be people you work/have worked with, those who you follow on social media or people who have published books & articles that you have read
Look at their job titles/places of work - are there people who have a similar job role to you, or one that you aspire to?
Are there people who have similiar research interests to you?
A couple of things to also consider is whether you want to meet your mentor face-to-face, or are you happy to have meetings via telephone or email (or maybe even Skype or Facetime)? Some mentors stipulate that they prefer to work with mentees in the same region, and others will only support those who are employed in the same organisation as themselves.
However you choose your mentor - good luck!