Pil

first make clear your mind on what issues you want to file under pil and it can be filed in High courts or Supreme court of India 

but for this you should be follow this steps

1.Make an informed decision to file a case. 

2.Consult all affected interest groups who are possible allies. 

3.Be careful in filing a case because 
i.Litigation can be expensive. 
ii.Litigation can be time consuming. 
iii.Litigation can take away decision making capability/strength from communities. 
iv.An adverse decision can affect the strength of the movement. 
v.Litigation involvement can divert the attention of the community away from the real issues.

4.If you have taken the decision
i.Collect all the relevant information 
ii.Be meticulous in gathering detail for use in the case. If you plan to use photographs, retain the negatives and take an affidavit from the photographer. Retain bills. 
iii.Write to the relevant authorities and be clear about your demands. 
iv.Maintain records in an organized fashion. 
v.Consult a lawyer on the choice of forum. 
vi.Engage a competent lawyer. If you are handling the matter yourself make sure you get good legal advice on the drafting. 
vii.A PIL can be filed only by a registered organization. If you are unregistered, please file the PIL in the name of an office bearer/member in his/her personal capacity. 
viii.You may have to issue a legal notice to the concerned parties/authorities before filing a PIL. Filing a suit against the government would require issuing a notice to the concerned officer department at least two months prior to filing.

Also, for frivolous litigation you can be fined heavily.

For filing PIL the applicant should be disinterested in subject matter and should not be frivolous and unlike other cases it cannot be withdrawn. It should involve substantial public interest.