the limitless right to live in Germany at the moment of applying for the citizenship, Blue Card or limited residence permit (Aufenthaltserlaubnis), in which it states the aim of the stay which can imply the longer term
successfully completed citizenship test (on the knowledge of German history, law, and public rules)
8 years of living in Germany (if one has successfully completed the integration course than he/she can apply after 7 years)
independent financial status for oneself and his/her family, that means that the family doesn't get any social support from the government nor does it get the unemployment benefits II
knowledge of German at a B1 level minimum
absence of any previous convictions;
in most of the cases renouncing the previous citizenship (there are some
exceptions, if you need a consultation on that, leave a message).