Lord of the Rings: War in the North is not particularly long, as RPG titles go, nor is there too much skill needed. The game does require 3 playthroughs however, one for each of its three difficulty modes. Also, there is one online trophy, which requires two other online players.

Expect roughly 30-35 hours of gameplay for the Platinum trophy.

You'll first want to play on Normal difficulty, from beginning to end. There are a number of story-related trophies you'll be unlocking along the way, as well as a few miscellaneous ones. Also, there is a trophy linked with each of the three playable characters. Since Farin is arguably the strongest character and so will be used in the second and third playthrough, we recommend focusing on unlocking the Herb-Master trophy for creating 15 potions with Andriel, then switch to Eraden until you've gotten the Seeker trophy for finding 25 hidden passages.

There are also four missable trophies which we recommend unlocking during your first playthrough. The Lidless Eye trophy for completing this sidequest by finding all seven unique scrolls, the Friend Of The Ring-Bearer trophy for speaking with Frodo at the beginning of Chapter 3, the Friend Of The Woodland Realm trophy for freeing the elf from the captors in the Woodland Marshes in Chapter 5, and the Eagle Savior trophy for NOT summoning Beleram during the final boss battle against Agandaur.

Once you've completed your first playthrough and unlocked a good chunk of the trophies, it's time to start your second on Heroic difficulty. Here, we recommend using Farin since his Explosive Bolt skill is highly effective. During this playthrough, try to mop-up any other miscellaneous trophies you still need. Be sure to check the Lord of the Rings: War in the North trophy guide links under our Links tab to see what you still need and their requirements.

After that, it's time for your third and, hopefully, final playthrough - this time on Legendary difficulty. Again, we recommend using Farin and work on any other remaining trophies.

Finally, at any point during your gameplay, you'll need to unlock the single online trophy, Strength Of Our Alliance, which involves slaying an enemy together with two other players. You will all need to hit the Triangle button at the same time to perform a critical hit. If you're having trouble finding players, check out the boosting forums under our Links tab.

IGN has a Walkthrough here:
http://www.ign.com/wikis/the-lord-of-the-rings-war-in-the-north/Getting_Started

And a Walkthrough by Josh Romero:
http://www.videogamesblogger.com/2011/11/01/lord-of-the-rings-war-in-the-north-walkthrough-video-guide-xbox-360-ps3-pc.htm

A text-based Walkthrough by Dragonfly13:
https://www.gamefaqs.com/ps3/991492-the-lord-of-the-rings-war-in-the-north/faqs/63532

dcollins22 has a great Trophy Guide here:
http://www.playstationtrophies.org/game/lord-of-the-rings-war-in-the-north/guide/

And a useful Trophy Guide by Fexelea:
http://fextralife.com/lord-of-the-rings-war-in-the-north-trophy-guide/

And an Achievement Guide (same as the trophies on PS3) by undoingduck and The Pants Party:
http://www.xboxachievements.com/game/lord-of-the-rings-war-in-the-north/guide/

A video demonstration of the Relentless trophy, by TrophiesAchieved:
https://www.youtube.com/watch?v=1M1-9dTKjq0

And a video demonstration of The Lidless Eye trophy, by LetsPlay Community:
https://www.youtube.com/watch?v=ncCqIv98gPM

And TrophiesAchieved has a video demonstration of the Friend To The Ring-Bearer trophy, here:
https://www.youtube.com/watch?v=-zaVb0zeOj4

A Boosting Forum on PlaystationTrophies:
http://www.playstationtrophies.org/forum/the-lord-of-the-rings-war-in-the-north/132427-co-op-partners-thread-read-first-post.html

And a Boosting Forum on PS3Trophies:
http://ps3trophies.com/forums/lord-rings-war-north/6287-official-lord-rings-war-north-boosting-thread.html

Finally, here's a basic Trophy List:
https://psnprofiles.com/trophies/1143-the-lord-of-the-rings-war-in-the-north