The deadline to file a California mechanics lien depends on your role on the project and whether a Notice of Completion was filed.
For GCs (and other that contracted directly with the property owner) the deadline is 90 days after project completion or, if a Notice of Completion is filed, then just 60 days after the notice was recorded.
For all other parties, the deadline to file is 90 days after project completion or, if a Notice of Completion is filed, then just 30 days after the notice was recorded. However, a lien cannot be filed by these parties until performance under their contract has ceased.
As far as the actual process of filing the lien, it's relatively simple but attention to details is crucial. You need to fill out all of the correct information, and get the claim filed with the county recorder's office where the property is located.