How do you file to enforce a Lien?

Mechanics liens all have an "expiration date" by which they must be enforced. If that deadline passes, the lien expires and becoems unenforceable. The deadline by which a filed lien must be enforced depends on the state in which the property was located / the lien was filed. 

Generally, once a lien is filed and notice of the filing has been provided to the property owner and other interested parties, the claimant can let it sit for a little bit in the hope that the lien filing itself will prompt payment in order to get the lien removed (and/or th elien complicates the project finances if it is ongoing).

However, eventually the lien will need to be enforced. A lien enforcement action is a full-blown lawsuit that could ultimately result in the foreclosure and sale of the property in order to satisfy the debt. As lawsuits take a lot of time and effort (not to mention potential expense), it is generally a good idea to hold off until it is clear that payment will not otherwise be forthcoming. In order to file an enforcement lawsuit, an individual lien claimant should (and a company lien claimant must) enlist the assistance of a lawyer.  

Generally, once the enforcement period has elapsed, the lien is expired and there's no going back (unless additional labor or material were furnished to the project at a later date tht may extend the time in which a new lien could be filed). In a few states a lien can be extended to lengthen the period in which the lien remain viable.

In states in which an extension of the enforcement period is not an option, other agreements (like a promissory note and voluntary encumberance like a deed of trust) can be used to gain security for repayment when the lien expires.