I echo Inch 100%. When I transferred to the RegF, I had eight years of Res Service. My policy was to keep my mouth firmly SHUT. The way I used my previous knowledge was to help the guys who were having trouble. No matter how bad the instruction got (and I saw some RegF instructors who, had they worked in my Pl when I was a WO, I would have sacked on the spot...), no matter how much I knew about what was being taught, I bit my tongue. One of my peers, a former Res Sgt, often failed to keep his yap shut and developed quite strong forearms from multiple pushups and running around with his rifle over his head.
(Mike O'Leary knows who I'm talking about.....)
The last thing the instructor (or the other recruits) want to hear is : "Well, when I was in the Royal Numptyville Fusiliers, we didn't do it that way yadda yadda yadda....". Do the best you can by putting your knowledge to good use, and the instructors will recognize your ability.
As for attitudes of people in the RegF: well... they're all humans. We'll probably never get rid of the Militia-haters, just like we'll never get rid of the Res people who see the Regs as a bunch of drunken layabouts who couldn't get "real" jobs. Cheers, and best of luck.