As my primary attack, I left the standard strike mapped to the left mouse button. From there I wound up with the smash on the button next to it. This arrangement worked out well both for initiating attacks and getting out of trouble if I needed to slow an enemy down a little to regroup. Then I left the other two on the number keys. As this description of skills probably gives away, combat has evolved beyond just smack it till it dies.
Tera winds up in a fairly unique middle ground between the multi-button combos of an action game and the click-on-icons-for-actions of a traditional MMO. Like the former, I needed to stay active around enemies, moving for good fighting position and watching their "tells"--signature animations that give away attacks--to know when to block(Tera online Gold). But like the latter, when I wanted to really get in some licks, I fired off my skills. In the end I wound up dancing around enemies a lot, hitting and blocking, but all the while keeping an eye on recharging skills to know when I could get in and hit them harder.
Once I got into the rhythm, I enjoyed the pace of the action. It's not without its challenges, though. The toughest I faced was using my chargeable skills while moving around. The whirlwind attack, for instance, could be charged by holding down the key. But since I'd mapped that to a number key, I had to twist my fingers to get down to WASD while holding Tera Gold down.