Start with the base
The magnet needs enough clean ferrous material and thickness to hold properly. Paint, scale, curvature, thin material and chips under the base can reduce holding force.
Match cutter and arbor
Use an annular cutter that fits the machine arbor and capacity. Inspect the pilot pin and cutter before starting.
Use cutting fluid correctly
Lubrication can extend cutter life and improve cut quality when the machine/cutter manufacturer calls for it. Keep chips controlled and never grab rotating swarf.
Secure the machine
Use the safety chain/strap where required. Do not rely on magnetic force alone when a falling drill could injure someone.
PPE and cleanup
Eye protection, hearing protection and appropriate clothing matter. Annular cutters can produce hot sharp slugs and chips.