Remove the spring coil mattress and box spring from the bed frame.
Grip the bed frame and move it back and forth to see if there are any loose joints.
Tighten any loose joints you have found on the frame using a flat-head screwdriver.
Place the box spring and mattress back onto the bed frame.
Lay on the bed, then shift your weight around to see if the bed still squeaks.
Measure the length and width of the mattress using a measuring tape.
Cut a plywood board that matches the measurements you took of the mattress. You can purchase plywood at your local hardwood store, and it can often be cut on site.
Place the plywood board in-between the mattress and box spring. This will help distribute your weight more evenly among the springs, reducing any noise that would be created.