Krishna Shashti is the name for the 21st Tithi (lunar day). It's the 6th Tithi of Krishnapaksha. It's nature is Yasha Prada, which can be interpreted as "one that gives fame". It's good for following works: house, land; service social customs; market & marketing, trade, sale - purchase; art; painting of sculpture; wood work; war, Alankar (ornament, decoration), deeds related to Pitris (ancestors); jewellery; clothes designing, oil massage; donation and welfare; actions related to water.
Referring to the most classical texts (Muhurta Chintamani, Poorva Kalamrita, Brihat Samhita) Karttikeya (Lord of valor) presides over this day and is favorable for coronations, meeting new friends, festivities and enjoyment.
Being Nanda (that can be translated as "prosperity", "good", "happiness") and ruled by Shukra (Venus), 6th Tithi of Krishnapaksha is suitable for following works or actions: related to clothes; dance, vocal music, festivals, art & sculpture, painting; farming, house, clothes, Alankar (ornament, decoration); enjoyments, Tantris Kāryas.
During the vedic month Magha Krishna Shashti becomes Maasa Shoonya Tithi, which is considered inauspicious in succeeding in works started during this Tithi.
Rohini Nakshatra becomes Tithi Shoonya if it falls on Krishna Shashti. It's considered that all auspicious works done during Tithi Shoonya periods will be destroyed.
If Sūrya (Sun) transits through Mesha (Aries) or Karkata (Cancer) during Krishna Shashti, it becomes Dagdha Tithi. Dagdha Tithis are known as inauspicious for starting any kind of work. Rishi (sage) Brihaspati also says that if Dagdha is present either for Lagna or Tithi then it inflicts death.