Shukla Ashtami is the name for the 8th Tithi (lunar day). It's nature is Dawanda Prada, which can be interpreted as "conflict or problem generator". It's good for works related to women, Alankar, enjoyment. It's auspicious for dancing, making and wearing jewellery, art, sculpture, painting, writing, house, foundation laying, war, government works and celebrations, trade, farming, stone, steel, water related works. Eating of meat should be avoided during this Tithi.
Shiva is Devata which rules the 8th Tithi of Shuklapaksha (referring to Muhurta Chintamani and Poorva Kalamrita), which is good for the destruction of any obstacle or enemy, overcoming of any problem and acts of combat. As per Brihat Samhita, Shukla Ashtami is ruled by Vasu and all actions done in respect of Vasu are more than acceptable.
Being Jaya (that can be translated as "victory" or "advancement") and ruled by Mangala (Mars), 8th Tithi of Shuklapaksha is suitable for following works or actions: weapon making; wars; training in army, collection of army, any matters related to power or strength; travelling; festival; medicine; trades; house matters; flags & conch-shell.
During the vedic months Chaitra and Margashirsha Shukla Ashtami becomes Maasa Shunya Tithi, which is considered inauspicious in succeeding in works started during this Tithi. Poorva Bhadrapada Nakshatra also becomes Tithi Shoonya if it falls on Shukla Ashtami.
Shukla Ashtami becomes Daghda Tithi (burned lunar day) for times when Surya (Sun) goes through Mithuna (Gemini) or Kanya (Virgo). It's considered that Daghda Tithis are inauspicious to start any type of work.