the bossmods will give you warnings about the boss actions (as you said, just before a boss does an action, or when cooldowns are ready etc.)
Often it will also tell you how you should react to that action, "Stop casting", "dont move" etc. Most also give you a range warning for those fights when you need to be at some distance from other toons.

If you want to know how to handle mobs though, like "dont try and aoe those mobs", then i think you'll need to check the websites like wowhead to get the boss strategies.