Repeating Istighfaar and Salawaat and Laa ilaaha illallah is very useful in cleaning the heart from the effect of bad acts and bad thoughts. Long Sojood is also very useful especially during night and when you are alone.
Visiting graveyard especially the graves of your parents and people whom you knew is also very useful for better spirituality.
Reciting Quran with clear voice or listening to Quran recitation is also helpful.
Repeating supplication and seeking from Allah to make your heart more clear is very good, e.g. RABBI ESHRAH LI SADRI WA YASSIR LI AMRI رَبِّ اشرَح لي صَدري ويَسِّر لي أمري