The first step when planning to remove shingles is to protect all the lower elements of the home or building. Cover air conditioners, doors, windows, plants, shrubs, etc. If there is bare ground or grass below and you don’t have an industrial magnet, you’ll also want to protect the grass/ground from nails falling and disappearing.
Use a roll off dumpster for old shingle disposal and place it below in the best position possible for receipt of old shingles from above. Setting roof jacks or standing supports will greatly improve your ability to maneuver around the roof and remove the shingles. These can be attached directly to the sheathing/roof framing below the old shingles (patch penetrations before re-roofing). A safety harness (or tie-off) is also another critical safety measure in case you slip and fall and don’t wish to go tumbling to the ground below.
Start at the ridge of the roof by tearing off the ridge caps and work your way downward. Use a shovel fork or roofing shovel to tear off the ridge caps/vents and shingles at the top. Pry the shingles up and remove. Some nails will come up with the shingle/felt assembly and others may stay in the sheathing.
Remove the shingles in sections working your way from rake to rake. You can also remove them from ridge to eave if desired. Be careful for rotted sheathing as soft spots are a hazard for falling through.
Clumps of shingles are a lot heavier than you might think; sometimes balling them up can help maneuverability. Keep your eyes out for rusted or cracked metal flashings as they should be replaced. Remove old ice and water barrier if you can, if it’s too stubborn to come off leave it. Valley flashing typically needs replaced with the shingles so pry up and remove this as well. Inspect the exposed roof sheathing for remaining nails and remove them. Don’t leave the roof exposed overnight as it will subject the house to possible moisture damage. Apply felt if possible or tarp until the felt can be applied.