I'm still just a few months in myself, though as I'm shopping I think: Could our pre-grain ancestors have eaten this? Your common sense, intuition and imagination are the best guides. Trust them, use them and they'll grow sharper and stronger.
Aside from that, read the "Top Posts" box in the right column. That's where I started (I also bought the book recently). One of those posts includes the Primal Blueprint Food Pyramid. Three months later and I've almost completely kicked the carb habit the big food companies worked so hard to curse me with since childhood. Only occasionally do I think, "I'd really like some junk food," but that usually passes when I eat pretty much anything else.
What I have found is while the initial path down Primal cooking is costly, many recipes here share ingredients so your grocery bills will level off (though they will always be more expensive... unless you factor in the money you will save on medical bills). Print enough to last a week. Go to your cabinet, bag up all grains and processed food and donate them to a shelter, then hit the store and buy ingredients you need for your new recipes.