Once, some PR instructor suggested I write down trigger words. This has made a world of difference. Even if you don't review them after you are done PR-ing and start activating, simply writing them down solidified the preview process in my mind.
Now, as I have gotten more proficient at PR-ing, I go back and look at the trigger words (like I think the book suggests) for ideas on what to activate.
Also, writing down your purpose can solidify it.
I know it can be a pain and seem montonous, possibly, but the extra few minutes will definitely be worth the effort.