Beginning Grimoire Hunting:
Okay, so step one is to identify what Dead Ghosts you are missing, as well as what Grimoire score you are missing. This is most easily done at DestinyTracker.com
For instance:
http://destinytracker.com/destiny/grimoire/ps/Kor_of_Memory
Use the [Missing Only] button at the top and see what I don't have. A quick scan shows that I need to generally play my Warlock and Hunter more and that I need to kill more Hydras and Ogres. Also, avoid Pulse Rifles if I can help it, since I have those maxed out already.
Now, if I Ctrl+F for Fragment, I see I'm missing 2 Dead Ghosts. Darkness 3, and Old Russia.
Now, we're going to compared that to this list here:
https://docs.google.com/document/d/1DQZTwmCgcOhhH0YiMta4oNTeNtpZ1L3MCDMsEgQgzAc/edit
It looks like both of my missing cards are on Earth, so I'll use the link at the top of the google doc to find them. Earth 4 and Earth 11 in this video:
http://bit.ly/rc_earth
Advanced Grimoire Hunting:
Most of the blocked off content in this game has a Dead Ghost floating around in it somewhere. While this ghost does not unlock any new Grimoire cards, it does add to your overall Grimoire Score. Here is where things get tricky.
You'll have to look up guides on how to break into areas that you shouldn't be in, some of them require teammates, so make note of that. Now, once you find out how to get into places, you're going to have to do some ghost hunting yourself. Thankfully most of the locations are small.
The most bang for your buck can be found in the Terminus. Basically a small jumping puzzle to get into, there are 3 easy to find Dead Ghosts in there.
Seraphim Vault (Part of the RAS-Bunker) has 1 ghost that I've found, but this area requires a second person to access. I've heard of a 2nd ghost here, but never seen one myself.
King's Watch I have never been in, but I've seen 2 ghosts in videos, and have heard of a 3rd. I'm wary to go into this location as apparently one of the dead ghosts actually awarded some players with a new ghost shell. Unfortunately, the Bungie BAN HAMMER scans for this and was banning accounts for obtaining said item. I believe you no longer receive the new Ghost Shell, but I stay away just in case. Not worth it in my Opinion.
Jovian Complex currently has no Ghosts in it.
The Black Garden secret area has no Ghosts in it.
I have not explored any of the Moon areas, as I figure I'll get to those in a couple of weeks anyway, and it's not worth the jumping puzzle headaches.
And that is pretty much everything I know about Grimoire score.