Well on the tactical standpoint
GSP is probably "preparing" for Shields for a long time, let's say he saw him coming, sitting on his throne. it's probably safe to assume that he had an underlaying workout during some time, aimed towards a fight like this (methodical and technical)
I feel GSP wants to make a statement and prove that he can finish fight (for some reason)
it's plain impossible to try and guess what GSP's gameplan gonna be. He might as well just go, roll and submit the guy (who thought he would mount fitch back in the days?)
or, he's planning on a stand up gameplan
I think NO ONE knows. So Shields probably worked a little bit of everything, while GSP most likely worked a LOT on sub defense and general grappling defense, and who knows what "a lot" means to a dude like this? For all that we know, he might as well pretty much mastered the whole thing by now and no one would have any idea of it until april 30th.
I'm pretty sure GSP in his interviews was working on building Shields confidence (saying he's somewhat "afraid" or he "doesn't take it lightly" etc...) in order to break it easily in the octagon.
I don't exactly remember which fight, GSP explained he did a specific kind of attack in order to weaked his opponent ability to grapple, we might see something like this again in the early rounds, but he'll probably hunt for the chin, I have the feeling he wants a KO here.
if he doesn't get the KO, he'll most likely frustrate Shields during the first 2 or 3 rounds, until he's softened enough.
then I see GSP taking this to the floor in the latter rounds so he can rashaad a decision
So I got GSP by KO/TKO in the early rounds
if he doesn't get it, he'll probably roll with a weakened/broken Shields up to the 5th bell and end up like getting a couple 10/8 rounds, the others being 10/9
I'm excited to see the fight because it'll all come down to "what if Shields surprises GSP?"
I don't rule Shields out because he's also fairly smart and probably sees a lot of things coming too.
but all in all I think GSP knows what to do and how to get the win here, while Shields is hoping he has a good gameplan and a good enough camp to get the work done.