My tips:
Save a lot coz sometimes you may feel like changing decisions. Also, save files do take up a lot of space.
You may want to check a guide sometimes coz sometimes you may let people die or kill them yourself who might have been very useful.
Enemy mages (usually with the suffix 'Emissary' without spoiling the game for you) are very difficult. If you have a Templar in party, make him learn the Cleanse Area spell. Very useful.
Buy backpacks wherever you find especially when its cheap.
A few mods I'd like to suggest: (nothing game changing, just some convenience, but should have been in the game in the first place)
http://www.dragonagenexus.com/downloads/file.php?id=664 http://www.dragonagenexus.com/downloads/file.php?id=1433 Also
CAUTION: If you didn't know yet, there is
friendly fire in DA: O. So, be careful.
Good luck and happy gaming.