Visit a law firm or Legal Aid Service Provider (if you cannot afford a private lawyer). You shall be interviewed to weigh the possibility of success or failure of your case.
If there are greater chances of success you can then give your instructions to your lawyer which are formalized through an engagement letter.
Before a lawsuit is instituted, the person suing (Plaintiff) is required to give a Notice of Intention to Sue or a demand notice to the other party (Defendant).
A Notice of Intention to sue takes on the form of an ordinary letter in which the Plaintiff states his/her demands and his/her intention to sue if those demands are not met within a certain time.
Upon the Defendant's failure to comply with the Notice of Intention to Sue/Demand Notice, a law suit may be then instituted by filing the necessary court documents that depend on the nature of claim.
NOTE: Failure to issue the notice of intention to sue dis-entitles a plaintiff who fails to issue that notice from getting the costs of the suit.