1 of the biggest things is rotating hurt units to the back of the firing line to spread damage out across your units, while also using proper focus fire on the enemy.
They also made it awesomely easy to build units while managing a battle. You can assign all unit production buildings to a single group, then tab through the different types of buildings to create the different units you need. If you have more then 1 of any given unit structure, then it will automatically split the unit creation assignments evenly between them.
Expansion bases is another major part of SC strategy. You need to expand fast enough and far enough to increase your resource farming while being able to also protect against harassment.
It's simple in many ways though as well, which is part of it's charm. Easy to learn, tough to master.
CoH is an awesome RTS though... Relic games in general.... I kinda like the DoW series which uses a lot of CoH's mechanics, and has more variety between factions