This isn't any more difficult than Half-Blood Prince, but more time consuming. Since the trophies related to the difficulty mode aren't stackable, you will need to play through three times, minimum. Any missed trophies along the way will require a fourth playthrough. Also, there are 4 online trophies which add another four or five hours to your gameplay, one of which requires a "friend" on your list to have this game.

Overall, expect over 20 hours of gameplay.

The trophies for completing each corresponding difficulty mode aren't stackable, which means you will need to play three times. Essentially, you'll want to start on Easy and work your way through, finding all the collectibles using a guide from our Links tab, and all the other trophies along the way. After this run, you should have the vast majority of the trophies unlocked.

Once that's finished, you can start on Medium. Here's your chance to gather any trophies you missed during your Easy run, as well as unlocking Auror Material for completing this difficulty mode.

Last, is Hard mode. Hopefully by this point, Order Of The Phoenix Recruit is the only offline trophy you need, which means just getting through to the end and completing your third playthrough. If not, try to unlock any other trophies you still need, so as to avoid a fourth playthrough.

A note about collectibles. If you find one, then die before the next checkpoint, you will need to pick up that collectible again. Otherwise, it won't count.

Last, are the four online trophies. These involve performing Online Challenges, and posting the results. Overall, these are not too difficult and can be collected within a few hours. For the Friendly Rivals trophy, you will need someone on your friends list to compare your rank with. If none of your friends out in the real world have this game, then you'll need to start making friends online, or check the boosting forums under our Links tab.

First, here's a Walkthrough with videos, by Rob:
http://www.videogamesblogger.com/2010/11/15/harry-potter-and-the-deathly-hallows-walkthrough-video-guide-wii-xbox-360-ps3-pc.htm

And another Walkthrough with videos, on Mahalo:
http://www.mahalo.com/harry-potter-and-the-deathly-hallows-part-1-walkthrough/

And a text-based Walkthrough, by dontyoulookatme:
http://www.gamefaqs.com/ps3/997204-harry-potter-and-the-deathly-hallows-part-1/faqs/61425

Here's a great Trophy Guide, by Hoagie324:
http://www.playstationtrophies.org/forum/harry-potter-deathly-hallows-part-1/79238-harry-potter-deathly-hallows-trophy-guide-road-map.html

And a detailed Trophy Guide here, by trophybot:
http://ps3trophies.com/forums/showwiki.php?title=PS3-Trophy-Guides:Harry-Potter-and-the-Deathly-Hallows-Part-1-Trophy-Guide

And an Achievement Guide (same as the Trophies on PS3) by TheHobbitGamer
http://www.xboxachievements.com/game/harry-potter-and-the-deathly-hallows/guide/

Here is a Collectibles Guide, by Hoagie324:
http://www.playstationtrophies.org/forum/1279895-post4.html

For that online trophy, here's a Boosting Forum on PlaystationTrophies:
http://www.playstationtrophies.org/forum/harry-potter-deathly-hallows-part-1/80483-trophy-boosting-thread-read-first-post.html

And a Boosting Forum on PS3Trophies:
http://ps3trophies.com/forums/harry-potter-deathly-hallows-part-1/6254-official-harry-potter-deathly-hallows-part-1-boosting-thread.html

Lastly, here's a basic Trophy List:
http://www.playstationtrophies.org/game/harry-potter-and-the-deathly-hallows-part-1/trophies/