Deliberate flanking maneuvers, an order of battle that puts heavier "shock" units up front that demand immediate attention while keeping units with equal or heavier firepower to the rear firing away, taking use of elevation, increased use of grenade...
Part of the problem is that even the "variety" of weapons, it comes down to a slugfest; there's not enough true variation, especially with regards to range. The only methods of differentiation there are in the game are damage, TU usage, and reduced or increased efficacy on certain types of enemies. If you're looking for enhanced tactics, you need a wider degree of variation and characteristics inherent to the weapon systems being used to maximize the range of tactics that can be implemented.
That said, a human player can scare you with units that pop out, sling some fire your way, and disappear, forcing you to either seek cover, or risk sending units out to eliminate that individual that's harrying you; this can be complicated by presenting additional units already there and engaging that force you to ignore the other enemy firing on you, or you might fall into a prepared ambush as you maneuver that unit. The "straightforwardness" of the enemy's behavior in X-COM doesn't quite lend itself to maneuver warfare or advanced "human" psychological tactics.
