Is it better to join Islamic groups or to be content with praying in the mosque, and if joining is better, then what are the best Islamic groups that one is advised to join?

A Muslim must adhere to Allah Almighty's command and cling to his religion, without deviating from it. This is aided by associating with righteous youth, cooperating with them in good deeds, and seeking knowledge. Belonging to da'wah groups is a means of steadfastness, and one must ensure that they adhere to the methodology of Ahlus-Sunnah (definition) wal-Jama'ah, and that their reference is the Quran and Sunnah according to the understanding of the Salaf. One must beware of fanaticism towards a particular group, for loyalty and disavowal are based on Islam, and the call is to the community of Ahlus-Sunnah, not a specific group. The truth in matters of ijtihad (definition) is not confined to one group, and a group must be advised if it errs. Knowing the truth and correctness is achieved by presenting matters to the Quran and Sunnah according to the understanding of the righteous Salaf.