Its hard to say much with all the different set-ups possible, different nations, different maps and different rares.
But for an early game turtle with focus on economy, the building placement is important. Early game HI can be handicapped by protecting cities with buildings. A city surrounded by buildings leave less room to attack. Basicly econ-buildings block on top left and top right side. Miningcamp is only econ-building that block on all 4 sides. So putting say a librarys topside next to wood, will block the path, or putting a turret between 2 well placed econ-buildings, will not only complete a wall, but also protect the turret from 2 sides.
Popping units in and out of building is elite, microing units like hell, say when attack animation begins, the damage has already been given, so you can right click it away immediately. (All units have an attack animation and a cooldown-period, where they cant attack again or garrison, by rightclicking it you save time, where you can move closer to a safe-city, or say move a cavalry closer to the next archer, or away from HI, very micro intensive I know)
Use civs to attack LI and archers(careful), also militia are only really weak to horse archers(until some late-game, cant remember) I always gets surprised by how fairly well militia do against cavs.(attrition eats civs/militia quick, so for defence only)
Focus-fire with city,on archers and LI, not on HI. (focus on the weak first, to kill em off)
Scouting is good, so you know what is coming, a late barrack with only a few soldiers in ur own camp is still more economically than what the rusher is doing, oh yeah use barrack to block as well
Thats all I can think of now..
Oh yeah, about right-clicking. right-clicking and hold down the button while dragging a bit is superior to normal right-clicking, because the game will not try to focus ur target or translate what action you want, it just moves the unit as close to the location as it can.[This message has been edited by I_like_BW (edited 05-07-2010 @ 07:49 PM).]