Shukla Saptami is the name for the 7th Tithi (lunar day). It's the 7th Tithi of Shuklapaksha. It's nature is Mitra Prada, which can be interpreted as "one that increases friends". It's good for following works: marriage; dance, music, singing; travelling; entering house; war, works related to elephants, jewellery making and wearing, hand works, Alankar (ornamentation).
According to Muhurta Chintamani and Poorva Kalamrita Surya is Devata which rules Saptami. Brihat Samhita mentions Indra, as a ruler of this lunar day.
Being Bhadra (that can be translated as "lucky") and ruled by Buddha (Mercury), the 7th Tithi of Shuklapaksha is suitable for following works or actions: marriage, Upanayana, ornament making and using, clothes; art; travelling by elephant or horses, travel, conveyance; making of roads; oil massage.
During the vedic month Magha Shukla Saptami becomes Brahma Savarni - Manvadi Tithi, which is considered to be extremely auspicious for any Punya Karma (Japa, Tapa, Dana, Havan, Homa etc.). But being Manvadi Tithi Shukla Saptami should be avoided in starting of education, Upanayana, marriage, ending of fasts, construction of house and entering thereof; travelling; plantation works.
During the vedic month Margashirsha Shukla Saptami becomes Maasa Shoonya Tithi, which is considered inauspicious in succeeding in works started during this Tithi. Lagna (ascendant or rising sign) during Shukla Saptami becomes Tithi Shoonya (Lagna which is ruined by Tithi) for times when it is Karkata (Cancer) or Dhanu (Sagittarius). Hasta and Moola Nakshatras also become Tithi Shoonya if they fall on Shukla Saptami. In classical texts it's mentioned that all auspicious works done during Tithi Shoonya periods will be destroyed.