It is highly advisable to engage yourself in  glorification of Almighty Allah and implorations for His forgiveness, because this hour is as important  as the pre-sunrise hour, as Almighty Allah has said in the Holy Quran:

وَسَبِّحْ بِحَمْدِ رَبِّكَ قَبْلَ طُلُوعِ ٱلشَّمْسِ وَقَبْلَ ٱلْغُرُوبِ.

And sing the praise of your Lord before the rising of the sun and before the setting.

Imam al-Sadiq (`a) is reported to have said, “When the color of the sun changes (i.e. the sun is about to set), you must remember Allah the Almighty and Majestic. If you are at that hour with one who preoccupies you from this, you must leave him and supplicate.

امْسَىٰ ظُلْمِي مُسْتَجِيراً بِعَفْوِكَ

amsa zulmi mustajiran bi`afwika

In this evening, my wrongdoing is taking shelter in Your pardon,

وَامْسَتْ ذُنُوبِي مُسْتَجِيرَةً بِمَغْفِرَتِكَ

wa amsat dhunubi mustajiratan bimaghfiratika

my sins are taking shelter in Your forgiveness,

وَامْسىٰ خَوْفِي مُسْتَجِيراً بِامَانِكَ

wa amsa khawfi mustajiran bi'amanika

my fear is taking shelter in Your security,

وَامْسَىٰ ذُلِّي مُسْتَجِيراً بِعِزِّكَ

wa amsa dhulli mustajiran bi`izzika

my humility is taking shelter in Your dignity,

وَامْسَىٰ فَقْرِي مُسْتَجِيراً بِغِنَاكَ

wa amsa faqri mustajiran bighinaka

my poverty is taking shelter in Your richness,

وَامْسَىٰ وَجْهِيَ ٱلْبَالِي مُسْتَجِيراً بِوَجْهِكَ ٱلدَّائِمِ ٱلْبَاقِي

wa amsa wajhiya albali mustajiran biwajhika aldda'imi albaqi

and my mortal face is taking shelter in Your Face, the Undying and Perpetual.

اللَّهُمَّ الْبِسْنِي عَافِيَتَكَ

allahumma albisni `afiyataka

O Allah, (please) dress me with Your wellbeing,

وَغَشِّنِي بِرَحْمَتِكَ

wa ghashshini birahmatika

cover me with Your mercy,

وَجَلِّلْنِي كَرَامَتَكَ

wa jallilni karamataka

overshadow me with Your honoring,

وَقِنِي شَرَّ خَلْقِكَ مِنَ ٱلْجِنِّ وَٱلإِنْسِ

wa qini sharra khalqika min aljinni wal-insi

and protect me against the evils of Your creatures—jinn and men.

يَا اللَّهُ يَا رَحْمٰنُ يَا رَحِيمُ

ya allahu ya rahmanu ya rahimu

O Allah! O All-beneficent! O All-merciful!

Continue the supplication to be said at sunset as under:

يَا مَنْ خَتَمَ ٱلنُّبُوَّةَ بِمُحَمَّدٍ

ya man khatama alnnubuwwata bimuhammadin

O He Who has sealed the Prophethood with Muhammad,

صَلَّىٰ ٱللَّهُ عَلَيْهِ وَآلِهِ

salla allahu `alayhi wa alihi

Allah may bless him and his Household,

إِخْتِمْ لِي فِي يَوْمِي هٰذَا بِخَيْرٍ

ikhtim li fi yawmi hadha bikhayrin

(please) seal with goodness this day of mine,

وَشَهْرِي بِخَيْرٍ

wa shahri bikhayrin

this month of mine,

وَسَنَتِي بِخَيْرٍ

wa sanati bikhayrin

this year of mine,

وَعُمْرِي بِخَيْرٍ

wa `umri bikhayrin

and my entire lifetime.