How would you introduce students to plotting points on a coordinate plane for the first time?

Immerse them in the experience. Using painter's tape(much better than masking tape for removing it cleanly) create a coordinate plane on the floor. Then make a game out of it having them move from the x negative and positive to the negative and positive . Have them go back to their seat and provide them drawing paper and have them draw the plane they moved through. Give them a game piece, or using their fingers and have them do the same thing in 2 dimensions. The next day, have them use that same drawing to label their lines with positive and negative numbers and the x and y. (Using graph paper will help them keep the numbers even spaced. Now using colored pencils have them mark dots/points of coordinates within the plane paying particular attention the the 0,0 or 0,-5 point types.