should I keep my Mac book pro plugged in whenever possible?

Leaving it plugged in will not overcharge the battery. Software lets the battery talk to the computer's power management system to prevent overcharging. Like a dog walking away from the food dish when he;s full.

Avoid running the battery to zero. I charge mine when the charge level is between 20 and 40 percent.

Some non-Apple battery sites recommend calibration. Apple stopped that recommendation about 2009. Calibration requires running the batter to zero, exactly what Apple warms against.