After the opening supplication, you should seek refuge with Allah from the devil, and doing so is obligatory. There are a number of ways from the Sunnah to do this; one of which is to say:

أَعُوذُ بِاللَّهِ السَّمِيعِ الْعَلِيمِ مِنَ الشَّيْطَانِ الرَّجِيمِ مِنْ هَمْزِهِ، وَنَفْخِهِ، وَنَفْثِهِ 

Transliteration: "a‛oodhu billaahis-samee‛-il-‛aleemi minash-shayṭaan-ir-rajeem, min hamzihi, wa nafkhihi, wanafthih"

Translation: I seek refuge with Allah from the accursed devil; from his suffocation, his arrogance, and his poetry.

Another is to say:

أَعُوذُ بِاللهِ مِنَ الشَّيْطَانِ الرَّجِيمِ

Transliteration: "a‛oodhu billaahi minash-shayṭaanir-rajeem"

Translation: I seek refuge with Allah from the accursed devil.