This may not be easy, as there are so many different practitioners available. If you can, get a personal recommendation under their belt. If you opt for counselling make sure you choose someone who is accredited with BACP(British Association for Counselling and Psychotherapy). An accredited member will have undertaken a full training programme plus some years of post-qualification practice.
If you choose a psychotherapist, make sure they are trained,qualified, experienced and registered with a national organisation such as UKCP which provides overall codes of ethics and practice and complaints procedures.
You can ask for an introductory session to see how you feel about them. If this is a big investment for you, choose someone who is both highly qualified and experienced and someone who you like and respect..