One of the most influential people I know once said "Believe it or not, those people out there [in the world] are just not paying attention" and its true, Derren makes the statement in the devils picturebook that you can basically give people instructions as to what to do, but make it seem like your not.
The methods are numerous, massively varying and wildly interesting, at least to me. My take on suggestion is that it requires an understanding of the way people work, and I don't just mean biologically. Whether you choose Jungian psychology, Leary's Eight Circuit Model, NLP's meta patterns/predicates/patterns for beleif stucture/etc or indeed any model of human neurology and combinations thereof as long as you have something that you can empirically determine to yourself as useful by testing it rigorously. The second requisite is methodologies whereby you can then begin to influence the system you understand, hypnosis and NLP are good methods or you may find something else.
I'll first point you to
http://www.saladltd.co.uk which is the web site for my NLP trainer, Jamie Smart. He sends out free weekly NLP tips to your email inbox and they are a great starting point for people interested in NLP, the backdated tips can be found in the archive. Other than those I'll list some books I have found useful.
Understanding people:
Quantum Psychology - Robert Anton Wilson
Prometheus Rising - Robert Anton Wilson
Kentonism - Kenton Knepper
WonderWords - Kenton Knepper
NLP at Work - Sue Knight
Also most things by Richard Bandler or to do with Milton Erickson.
Hope that helps you climb some steps.
Gaz