Firstly: they refrain from transgressing the boundaries of knowledge, they speak with that which they have knowledge of, and refrain from speaking about that which they do not have knowledge of. Allāh mentions:

وَلا تَقْفُ مَا لَيْسَ لَكَ بِهِ عِلْمٌ
And do not pursue that of which you have no knowledge.
[Al-Isrāʾ, 17:36]

This means that one must not falsely accuse or say something of which he has no knowledge of about Allāh. Rather, stop at your limits, if you know something of beneficial knowledge then speak with it, and if you know not about something then refrain (from speaking about it) until you gain knowledge regarding it. This is the way of Ahl al-Īmān.

Secondly: from the signs (of Ahl al-Sunnah wa-al-Jamāʿah) is that they resort to [utilising] the ḥalāl whilst doing away with the ḥarām. They utilise the good whilst doing away with the bad with regard to their foods, drinks, clothes, and marriages. They confine themselves to that which Allāh has made ḥalāl for them and they refrain from that which Allāh has made ḥarām for them. Allāh mentions describing the Messenger (ﷺ):

وَيُحِلُّ لَهُمُ الطَّيِّبَاتِ وَيُحَرِّمُ عَلَيْهِمُ الْخَبَائِثَ
And makes lawful for them the good things and prohibits for them the evil
[Al-Aʿrāf, 7:157]

Source: Bayān al-Mʿānī fī Sharḥ Muqadimāh Ibn Abī Zayd al-Qayrawānī, pg.17-18.
Translated by: Munīb al-Ṣumālī