The truth is that we all experience the highs and lows of Iman at some point in our lives. However, the important thing is to remember that Allah (SWT) doesn’t expect perfection from us at all times. In fact, He just wants us to try our best. 
Striving to become better Muslims by making small changes in our lives is an achievement in itself. Therefore, when we see our Iman weakening, let’s start by taking these 4 small steps that bring us closer to the Almighty Allah, as defined in the Holy Qur’an:

1- Believe In Allah (SWT)’s Mercy
“Allah is the Ally of those who believe. He brings them out from darkness into the light.”
– Surah Al-Baqarah: 257

2- Pray
“And establish prayer and give zakāh and bow with those who bow [in worship and obedience].”
– Surah Al-Baqarah: 43

3- Make Dua
And your Lord says, “Call upon Me; I will respond to you.”
– Surah Ghafir: 60

4- Give Charity
“Those who spend their wealth [in Allah's way] by night and by day, secretly and publicly - they will have their reward with their Lord. And no fear will there be concerning them, nor will they grieve.”
– Surah Al-Baqarah: 274

May Allah (SWT) strengthen our Iman and reward us with the best of both worlds. Ameen.