Who must serve it
Direct contractors who sit on a contract with the owner often have a different notice path. Subcontractors and suppliers typically must serve a preliminary notice within 20 days of first furnishing labor or materials. Serve late and you generally protect only the work from 20 days before the notice forward — earlier work drops out.
Who gets a copy
Owner, original contractor, and construction lender if there is one. Missing the lender is a frequent, expensive miss on jobs with a construction loan. Use the addresses on the building permit and the recorded deed, not the superintendent's cell phone.
Then keep the second clock
The preliminary notice does not record a lien. It preserves the right to record one later under § 8400. Calendar completion, notices of completion, and the 90- or 30-day recording window the day you serve.