Improved Rend is a terrible waste of points. After level 20 or so, rend loses it's charm and should be taken out of regular rotation (only used in PvP to keep a rogue from vanishing or to make sure someone can't bandage).
For leveling, improving your heroic strike and/or parry are the way to go if you want to level as arms. If you are going fury, I like
this build as something to build up to 40 (for 2-handers, not dual wield). The second tier is personal preference, but Unbridled Wrath is not as impressive with a slow weapon as two faster weapons. This build is based on using a heavy-hitting 2-handed weapon and (after 30) hitting your 0.5 sec Slam after every auto-attack.
However you decide to level, remember that there's the ability to pay to refund your talent points at any point in the game. Part of the leveling process is learning your class and what abilities are worth improving through talents. It also may change over time, so don't be afraid to pick up a talent that works for now but will be useless later (other than improved rend... it becomes obsolete very, very fast).