Try doing it slowly, don't go out sparring thinking "I'm going to trap this guy all day long until he won't dare to even punch". That's not a good attitude. Trapping happens when he starts guessing and is really defensive.
So my advice, be offensive and defensive all the time. Suddenly attack, then retreat, attack, retreat, until you feel he's starting to know your rhytm, and now you attack or feint, and DON'T retreat, he'll be thinking, you will retreat but you're not, and then well, do your stuff, trap, block, throw, counter, parry, whatever.
This tactic doesn't work on overly aggressive people that don't care if they get hit, mostly MMA, grapplers and some stand-up fighters like MT, Stalker Boxer[Foreman/Tyson style]. When you punch or feint, they won't flinch, the'll sometimes happily recieve and give back more. It's called Drunken Boxing or Interchange boxing, or more rudely, Fisting exchange.
Good Luck and try think clearly, or don't think at all, your body will start doing its stuff instinctly after a few weeks?
-Taison