Richard Bandler, the father of NLP, would probably spank me if I would say NLP is the twin of hypnosis. Anyway, all I can say is NLP is highly effective.

You can do it on yourself, but it works much better if you are only a client, otherwise you are too attached to the problems you are looking to solve and that gets into the way (with some of the nlp techniques, not all). I know from practice that many good NLP practitioners where unable to help themselves and needed to get external help for their own problems. Again, all this does mean is just that NLP is more effective if other person does it on you, than if you are applying in on your own as a self-help.

Result of few NLP sessions always depends on the capability of the therapist. It doesn't matter whether they have diploma, what matters bit more is who certified them, which kind of course it was, how long it took, and what matters in first place, what results do they achieve with their clients in their day-to-day work. For the starters and self-help, you can use one of many available good introductory NLP books. The basic techniques might be enough in many cases, if you find persistence in doing them and ability to follow up on all the instructions step by step.

As a first step, I recommend some of the good books. Information available on the internet is IMHO not as suitable as one would like. Get NLP in 21 days by Harry Alder, NLP The New Technology of Achievement by NLP Comprehensive team, or the all times classic Introducing Neuro-Linguistic Programming from Joseph O'Connor and John Seymour. These all are fine beginners book that will save you a lot of time that you would otherwise spend hunting for incomplete information on the internet.