The most excellent fast after Ramadan is God's month. al-Muharram, and the most excellent prayer after what is prescribed is prayer during the night.  

قَالَ رَسُولُ اللَّهِ ﷺ أَفْضَلُ الصِّيَامِ بَعْدَ رَمَضَانَ شَهْرُ اللَّهِ الْمُحَرَّمُ وَأَفْضَلُ الصَّلاَةِ بَعْدَ الْفَرِيضَةِ صَلاَةُ اللَّيْلِ  

The Prophet ﷺ never fasted in any month more than in the month of Sha'ban.

He used to say, "Do those deeds which you can do easily, as Allah will not get tired (of giving rewards) till you get bored and tired (of performing religious deeds)." The most beloved prayer to the Prophet ﷺ was the one that was done regularly (throughout the life) even if it were little. And whenever the Prophet ﷺ offered a prayer he used to offer it regularly.  

لَمْ يَكُنِ النَّبِيُّ ﷺ يَصُومُ شَهْرًا أَكْثَرَ مِنْ شَعْبَانَ فَإِنَّهُ كَانَ يَصُومُ شَعْبَانَ كُلَّهُ

وَكَانَ يَقُولُ خُذُوا مِنَ الْعَمَلِ مَا تُطِيقُونَ فَإِنَّ اللَّهَ لاَ يَمَلُّ حَتَّى تَمَلُّوا وَأَحَبُّ الصَّلاَةِ إِلَى النَّبِيِّ ﷺ مَا دُووِمَ عَلَيْهِ وَإِنْ قَلَّتْ وَكَانَ إِذَا صَلَّى صَلاَةً دَاوَمَ عَلَيْهَا  

The father or Uncle of Mujibah al-Bahiliyyah visited the Messenger of Allah ﷺ. He then went away and came to him (again) after one year when his condition and appearance had changed. He said: Messenger of Allah, do you not recognize me? He asked: Who are you? He replied: I am al-Bahili who came to you last year. He said: What has changed you? You were looking well, then you were good in appearance? He said: I have only food at night since I departed from you.

Thereupon the Messenger of Allah ﷺ said: Why did you torment yourself? Fast during Ramadan (the month of patience) and fast for one day every month. He said: Increase it for me, for I have (more) strength. He said: Fast two days. He again said: Increase it for me. He said: Fast three days. He again said: Increase it for me. He said: Fast during the inviolable months and then stop; fast during the inviolable months and then stop; fast during the inviolable months and then stop. He indicated by his three fingers, and joined them and then opened them.  

أَنَّهُ أَتَى رَسُولَ اللَّهِ ﷺ ثُمَّ انْطَلَقَ فَأَتَاهُ بَعْدَ سَنَةٍ وَقَدْ تَغَيَّرَتْ حَالَتُهُ وَهَيْئَتُهُ فَقَالَ: يَا رَسُولَ اللَّهِ أَمَا تَعْرِفُنِي؟ قَالَ: «وَمَنْ أَنْتَ؟» قَالَ: أَنَا الْبَاهِلِيُّ الَّذِي جِئْتُكَ عَامَ الأَوَّلِ۔ قَالَ: «فَمَا غَيَّرَكَ وَقَدْ كُنْتَ حَسَنَ الْهَيْئَةِ؟» قَالَ: مَا أَكَلْتُ طَعَامًا إِلاَّ بِلَيْلٍ مُنْذُ فَارَقْتُكَ۔ فَقَالَ رَسُولُ اللَّهِ ﷺ: «لِمَ عَذَّبْتَ نَفْسَكَ؟»

ثُمَّ قَالَ: «صُمْ شَهْرَ الصَّبْرِ، وَيَوْمًا مِنْ كُلِّ شَهْرٍ۔» قَالَ: زِدْنِي فَإِنَّ بِي قُوَّةً۔ قَالَ: «صُمْ يَوْمَيْنِ۔» قَالَ: زِدْنِي۔ قَالَ: «صُمْ ثَلاَثَةَ أَيَّامٍ۔» قَالَ: زِدْنِي۔ قَالَ: «صُمْ مِنَ الْحُرُمِ وَاتْرُكْ، صُمْ مِنَ الْحُرُمِ وَاتْرُكْ، صُمْ مِنَ الْحُرُمِ وَاتْرُكْ۔» وَقَالَ بِأَصَابِعِهِ الثَّلاَثَةِ فَضَمَّهَا ثُمَّ أَرْسَلَهَا