The first thing a Muslim has to do is to know the sound `Aqidah and adhere thereto. Allah (Exalted be He) says:
So know (O Muhammad صلى الله عليه وسلم) that, Lâ ilâha illallâh (none has the right to be worshipped but Allâh), and ask forgiveness for your sin, and also for (the sin of) believing men and believing women.
Therefore, (Part No. 2; Page No. 27) Allah's Messengers (peace be upon them) would start their mission by calling people to the sound `Aqidah, which is worshipping Allah Alone, associating no partners with Him. Allah (Exalted be He) says:
And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): “Worship Allâh (Alone), and avoid (or keep away from) Tâghût (all false deities i.e. do not worship Tâghût besides Allâh).”
In fact, Islamic government is a part of the `Aqidah but it is not everything thereof.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.