This is one of the few first-person shooter titles in which the offline trophies are just as challenging as the online. Playing the game on its hardest difficulty setting - Elite - can be arguably considered one of the toughest FPS games to clear.

With a boosting partner, this difficulty rating could be dropped to a 4-star, but reaching the top 1% is still very time consuming, and needs to be concentrated within one week. Even with a boosting buddy, this is certainly one difficult Platinum to obtain - but one to be proud of.

We recommend beginning your playthrough on Easy. For one thing, as long as you finish the game - regardless of the difficulty mode - you will still unlock Elite difficulty. Also, there are a number of trophies, such as completing all missions without dying for Untouchable, and several timed boss trophies, which can be challenging to accomplish on a higher difficulty mode. So, play through from beginning to end, doing your best not to die, try to unlock trophies related to the timed bosses, as well as work through getting the kill-related trophies nad finding intel along the way.

After that, you can mop up by replaying missions. You can replay ones you've died on, as well as ones you're missing intel or any other random trophies. After your mop-up run, you should have all the trophies except for Heroic Survivor and the online ones.

Next, load up a game on Elite difficulty and prepare for a challenging playthrough. If there's parts of the game that are overly frustrating, you can always use the Mission Select to complete them in any order.

After you completed Elite difficulty, then congratulate yourself on a job well done. No one considers that easy. Unfortunately, you still have the remaining 10 online trophies to unlock. If you can find two or three people to boost with, you can set up private matches and boost for reaching the top 1% for that week. This means, playing nearly every day for seven days. If you're not boosting, then you'll need some serious FPS skills to unlock these online trophies.

Good luck!

IGN has a useful Walkthrough, here:
http://www.ign.com/wikis/killzone-2/Walkthrough

And a Walkthrough here, by Andre Segers:
http://www.gamespot.com/articles/killzone-2-walkthrough/1100-6205187/

Ratchet12345 has a great Walkthrough, here:
http://www.gamefaqs.com/ps3/928377-killzone-2/faqs/56524

Here's a great Trophy Guide by Sarnath and mjc0961, which includes the DLC:
http://www.playstationtrophies.org/game/killzone-2/guide/

And a detailed Trophy Guide here, by trophybot:
http://ps3trophies.com/forums/showwiki.php?title=PS3-Trophy-Guides:Killzone-2-Trophy-Guide

And a useful Trophy Guide by Jeff Belote:
http://www.playstationlifestyle.net/2009/03/12/trophy-guide-killzone-2/

A simple but useful Trophy Guide here, by AndyBSG:
http://community.eu.playstation.com/t5/Killzone/Killzone-2-Trophy-Guide-amp-Tips/td-p/7681906

xstation360 has a video guide showing all the Intel and Symbol Locations:
https://www.youtube.com/watch?v=6qWJoR2L98s

And a video by PringlesForAidan, demonstrating the Barrel Of Death trophy:
https://www.youtube.com/watch?v=E9ry038Ghbs

And PringlesForAidan's video demonstrating the Dragonslayer trophy:
https://www.youtube.com/watch?v=hsI4IGLFMZ4

Here's a list of the Ribbon Requirements, posted by Savenger:
http://www.playstationtrophies.org/forum/killzone-2/15273-online-ribbon-requirements.html

For those online trophies, here's a Boosting Forum on PS3 Trophies:
http://www.playstationtrophies.org/forum/killzone-2/2636-trophy-boosting-thread-read-first-post.html

Finally, here's a basic Trophy List:
http://www.allps3trophies.com/retail-games/killzone-2-trophies.html