There is an order in which you must take your skills. Leave Sharpen Blade at level 1 until you get your guardian skills. The reason being that it's totally useless for lower levels and doesn't take into account the bonus you get from your dagger. It isn't going to make your break your build to leave it at 1 early on and the skill points can be used elsewhere.
Once you hit guardian, straight away max out Sword Mastery and Physical Blow. by time you're 50 you should have some decent weapons.
Add one Point into Taunt roar, as it's necessary to access the rest of the tree.
Immediately max out Crazy Strength and Rush at 54.
At 56 only put one point into Final Crash and Blue Drain. Max out Crazy Standing. Blue drain is a great skill, but again, you have more important skills to get.
At 58 grab both Order Swing and Critical Aura. Order Swing is more important than critical aura simply because it's part of the guardian's main combo. Critical aura is great to have because it adds a boost in the spike damage you deal. Your overall DPS will go up.
At this point get one point in Roha's Blessing, Knight Symbol and Stone Skin. Go back and max out Sharpen Blade.
The rest of the tree you can fill pretty much at your leisure. I highly recommend Heavy Weapon and War Cry. The combination of those skills will allow you to dominate /any/ melee class that dares to face you head on.
If you followed this guide, once you hit level 100, you should be able to max out heroic power immediately. The same for stunner at 101. Stunner makes it possible for you to keep people under stun for a whole CS. You no longer have to roll with a shield. I still recommend it though. Shields are good for tanking and if you get the optional skills for it will make it really useful as well.
I didn't include these in the guide because they are purely optional. They are useful or cool in their own way. If you followed the guide you should have more than a few points to spare by endgame.
A nifty little skill to play around with. On the off chance you crit with it, you may deal some serious damage. Not worth investing more than a single point in if at all.
I love this skill. If you have some hp/mp leech on your weapon it will allow you tank larger mobs than usual. Personally I keep this at level 1.
Good way to charge OS and deal damage. The animation also looks cool to boot.
Taking this skill is necessary to unlock Order Swing, but you may max it out as well. Like Straight Repulse it's a great damage dealer and another way to charge up OS.
If you're taking shield skills you have to take this one. Pumping it up to level 5 adds damage that you simply negate. Combined with a Molly I think it's around 1/4 of all melee attacks that don't hit you. Additionally you can leave it at level 1 just to get access to the next stun.
Another stun you can take in addition to your regular ones. Not worth getting past level 3 unless you SES it.