theory11 — Magic Tricks & the World's Finest Playing Cards

Anchoring

Pretty well every basic NLP (neuro-linguistic programming) book shows you how to do it, I find NLP improves a mentalism routine 100 fold.
 
Derren Brown also explains it well in "Tricks of the Mind". But honestly, it's another form of suggestion. It works a slightly better than a straight suggestion simply because you cause a physical connection.