I've been playing Pathfinder off and on for a couple years now, and am fairly familiar with the rules. I also heard from my brother that Pathfinder came into being as a better version of Dungeons and Dragons (no offence to DnD players). I also happen to be going off to college soon, and they have a Dungeons and Dragons club there and they use Dungeons and Dragons 3.5e. So this got me thinking: what is the most hassle and confusion free way to transition from Pathfinder to Dungeons and Dragons 3.5e so that way I won't make a complete fool of myself right when I start college?
In addition to Vorpal Mischa's answer, this question has proven to be quite useful for anyone who transfers between the two systems.
Just to mention the most important changes: In D&D, characters can generally take less of a beating than in Pathfinder, so you might need to adjust your combat techniques.
Further, Grappling and Tripping are a little more complicated in D&D 3.5 than they were in Pathfinder, so if you desire to play a Combat Manouver-heavy character, familiarize yourself with these rules before.
many some regard Pathfinder as being "more balanced", so your favourite class/race/build/etc. might be much stronger or much weaker in comparison to how they performed in Pathfinder.
3.5 and Pathfinder are incredibly similar, which can make the transition easy in overall knowledge, but you may find yourself tripped up with specifics and small details. You may often find yourself remembering Pathfinder specific details and stats which aren't present in 3.5e, or slightly different.
I'd advise you make sure to double check everything for a start - no matter how simple - just to be sure, and to tell your fellow players that you're from a Pathfinder background, and encourage them to point out your errors. If you have the time, it might be worthwhile to get them to quickly check over your character sheet to make sure you haven't mixed up systems.