In Hindu mythology, every day of the week is dedicated to one particular god. Devotees who believe in god worship particular lords every day. So, if you want to worship all avatras and forms of god in particular, you get one whole day to shower your devotion to the god! In short, every day of the week is dedicated to a particular god. For example, Monday is a day which is devoted to Lord Shiva. Tuesday is the day to worship Lord Hanuman, Wednesday to Lord Ganesha etc.
Monday: Lord Shiva
You will see immense crowd in Shiva temples especially on Mondays. This is
because it is the day to worship the Neelkanth. Offer milk, rice and sugar to
Lord Shiva.
Tuesday: Lord Hanuman
The Monkey God is worshiped on Tuesdays. He is considered as the the lord of
strength, and is considered as an incarnation of Lord Shiva.
Wednesday: Lord Ganesha
He is the remover of all obstacles and Wednesday is the best day to worship
Him.
Thursday: Lord Vishnu
Lord Vishnu is worshiped on Thursdays. It is also a day to worship Vishnu's wife,
Goddess Lakshmi. It is said that Thursday is an auspicious day to worship the
Lords of fortune and wealth.
Friday: Goddess Durga
Goddess Durga and her avatars are worshiped on Friday. It can also be
considered as a day to worship all the avatars of God in unison.
Saturday: Shani Dev
Saturday is also associated with Saturn which is ruled by Shani Dev. On Saturdays, Shani Dev, Lord Hanuman and Goddess Kali are worshiped by devotees.
Sunday: Surya Dev
The Lord of fame and the chief of the Navagraha is worshiped on Sunday. Make
sure you offer water to the sun, and chant the Gayatri Mantra on Sunday
morning.