Mark the cut line with a fine-tip marker and straightedge
Leave the protective film on the plexiglass if possible
Clamp the sheet securely to a stable work surface
Score thin plexiglass repeatedly with a utility knife and straightedge
Snap the sheet cleanly along the scored line
Use a fine-tooth saw for thicker plexiglass
Use a jigsaw with a blade made for plastic
Use a circular saw with a fine-tooth blade for straight cuts
Cut slowly to reduce chipping and cracking
Keep the blade moving steadily without forcing it
Support both sides of the cut to prevent vibration
Use masking tape along the cut line to help reduce splintering
Sand the cut edge with fine-grit sandpaper
Wear safety glasses and gloves
Work in a well-ventilated area
Let the material cool if it starts to melt from friction