Keep one entry per event
Date, symptom, contractor, diagnosis, work completed and final cost are enough for most repairs.
Attach evidence
Invoice, warranty, permit, inspection and photos belong with the entry.
Record model numbers
Mechanical equipment and appliances are much easier to service when identity is known.
Keep superseded information
Knowing what was replaced and when can explain later changes.
Safety boundary. General planning information only. Do not open, dismantle or work on hazardous electrical, gas, structural, fire-protection or contaminated-water systems unless you are appropriately qualified and authorized.