New and old players alike often lapse their concentration on important matters when concentrating on what they deem to be higher priorities. The problem is that often where they are spending their attentions does not require that amount of focus they are dedicating to it.
When moving out with your army, you don't -need- to hover your screen over them all the while. Send a worker, observer or single unit from the composition further ahead to scout for you. This enables you to continue macroing right untill the point where your minimap flashes red (The scout gets attacked, or sees enemy forces).
Create an expansion just before you push out. It allows you to get ahead economically during and after the fight for minimal effort. If you lose the fight, they will most likely go straight to your base and not see it. If you win they have little chance of finding it untill rebuilding their forces.
During a battle, you don't need to micro all the time if you can avoid it. Once the concave is set up, make use of shift queued commands to cast abilities and focus fire. Watching the battle the whole time allows you to pull injured units out and back in, but you may be missing out on all of the reinforcements you will need whether successful or not. Too many people suffer from this and amass minerals during fights.
Make use of the F1, F2, F3 etc. Hotkeys to highlight important locations and quickly return to them, it works better than devoted hotkeys to unit production. You can use these to map areas fights are most likely to occur, the enemy base to recheck what tech they have after each scouting and your expansions.