I'm giving away my age, but here are two tricks lost to modern instructors. To write legibly on a chalk board, you have to take an eraser, tap it in chalk dust, then wipe down the green- or black-board to "season" it so the board doesn't grab the chalk while you're writing. Helps avoid the dreaded chalk squeak, and is particularly important if a janitor has just cleaned the board for you.
Reverse the trick for white boards by wiping down with alcohol to remove oils and help it grip the marker better. If you're cursed with a whiteboard, do remember the wise words of Bill Clinton: Don't inhale.
Every teacher should get to use a chalk board. Not only am I unsure of what the marker fumes did to my brain while teaching, but classroom control is much easier with a chalkboard. Just claw your fingers, poise them over the blackboard, clear your throat, and classroom control is yours again.
ALT Photo of a man in front of a chalkboard.