Since your category says, "mental health," it's safe to assume this is what your question pertains to...?......
I can tell you it is of utmost importance to find a well-qualified, experienced professional......do your homework. Many Therapists will advertise their "specialty," eg., family, marital, addiction, behavior etc. This is a clear indication that this is what they do most often and as a result, do it best.
Don't go into therapy expecting miracle results nor overnight cures. It simply doesn't work that way. Be aware that therapy works best when you fully cooperate with your therapist or counselor.
The most valuable advice I want to share with you, Nicola, is to give a particular therapist, at least three sessions, before you determine whether you LIKE him/her...are comfortable with them and are able to feel a bit better, after each visit. After that 3rd. visit, if you do not wish to stay with him/her.....immediately find a replacement. Choosing to seek therapy can be the single-most sensible and healthy thing you can do for yourself. When done well and long enough, it is life-changing.