Route Planning

Question for folks who've done this a heck of a lot more than me.

How do you plan routes? I have a PA28-180/G that I fly. The navdata is
always kept up to date so I can always file /G. Which I suppose might be
the best answer here. But the vagaries of ATC, especially in the
Northeast US make me wonder just how does the system work? I'd like to
understand this because it can make getting my clearances a heck of a
lot easier and efficient. Most of my x-ctry flights will be between 75
and say 200NM.

Another difference I've noted is getting my clearance on the ground
before takeoff out of KFIT (uncontrolled field) versus getting my
clearance in the air while in VFR but en route. Let's say I want to fly
IFR from KFIT to KBDL. I would file GDM V106 BAF BDL, if I get my
clearance in the air it would be one thing, if I got it on the ground
Boston Appch would have me go right turn 090 climb and maintain 4000
then hand me off. In other words, turn the wrong direction east rather
than west.

Then there is the whole question of TEC versus IFR Preferred Routes. Are
there references available that talk about how this factors into route
planning?

Thanks for any and all input,
KC