Use a stud finder and move it slowly across the wall
Tap the wall and listen for a solid sound instead of a hollow one
Look for electrical outlets, which are often attached to studs
Measure 16 inches from a known stud center to find the next one
Check for baseboard nails or trim nails that may indicate stud locations
Use a small finishing nail or pin to probe for solid wood
Mark the stud edges and confirm the center before drilling or hanging anything