On Dwaadashee, one should take A-Yaachit food only one time in the night. If somebody eats food asked in alms and keep fast on Dwaadashee, his fast will not be successful.

Akhand Dwaadashee Vrat
Maargsheersh Shukla 12th. This Dwaadshee bestows lots of Punya, if kept fast and worshipped Vishnu on this day. Vratee should take bath with Panchgavya mixed water and do Paaran with that water only. Donate a pot filled with barley and pray - "Hey Bhagavan, Whichever Vrat has not been done properly during my last 7 lives, they all become proper (complete) and give me unbroken fruit. As you are present in this world in your unbroken form, in the same way my all Vrat should also be unbroken." Thus beginning from Maargsheersh and ending in Phaalgun, it should be done every month for four months. When it is done from Chaitra to Aashaadh, donate a pot full of Sattoo. Or it can be done from Shraavan to Kaarttik also.
[Agni Puraan, 21]

Anant Dwaadashee Vrat
On Bhaadrapad Shukla 12th.
[Agni Puraan, 21]

Bheem Dwaadashee Vrat
On Maagh Shukla 12th, keep fast, and worship Vishnu with "Namo Naaraanaaya" Mantra. One gets all by doing this.
[Agni Puraan, 21]

Govats Dwaadashee Vrat
On Bhaadrapad Shukla 12th. Who keeps fast on this day, he should worship calf.
[Agni Puraan, 21]

Govind Dwaadashee Vrat
On Phaalgun Shukla 12th.
[Agni Puraan, 21]

Maargsheersh Dwaadashee
Who keeps fast on Maargsheersh Shukla 12th, and donates salt after worship Krishn, he gets the fruit of donating all kinds of juices.
[Agni Puraan, 21]

Madan Dwaadashee Vrat
Chaitra Shukla 12th is called Madan Dwaadashee; and one should worship Kaam Dev who has the desire of pleasures and Moksh.
[Agni Puraan, 21]

Mahaa Dwaadashee Vrat
It is known as Jayaa, Vijayaa, Jayantee and Paapnaashinee with the Yog (combination) of various Nakshatra :-
--Jayaa - When there is Punarvasu Nakshatra on Shukla Ekaadashee, it is called Jayaa Dwaadashee.
--Vijayaa - When there is Shravan Nakshatra on Shukla Dwaadashee, it is known as Vijayaa Dwaadashee. Daan and feeding Brahman on this day give thousand times more fruits.
--Jayantee - When there is Rohinee Nakshatra on Shukla Dwaadashee, it is called Jayantee Dwaadashee.
--Paapnaashinee - When there is Pushya Nakshatra on Shukla Dwaadashee, it is called Paapnaashinee Dwaadashee. Who donates 1 Prasth sesame seed everyday for one year, and who keeps fast on Paapnaashinee Ekaadashee, both give equal fruits. If worshipped, Shree Hari is pleased and may give His Darshan too. All Punya done on that day give eternal fruit. One can get one thousand Ekaadashee Vrat fruit by doing this Vrat only. One must keep this Vrat.
[Padm Puraan, 5/4, p 643]

Manorath Dwaadshee Vrat
Phaalgun Shukla 12th is called Manorath Dwaadashee. Keep fast on this day and worship Hari.
[Agni Puraan, 21]

Naam Dwaadashee Vrat
Phaalgun Shukla 12th, who keeps the fast for  Naam Dwaadashee, should worship Hari with "Keshav" name for 1 year. He can never go to Narak.
[Agni Puraan, 21]

Sampraapti Dwaadashee Vrat
On Paush Shukla 12th.
[Agni Puraan, 21]

Shravan Dwaadashee Vrat
On Shraavan Shukla 12th. It is good when it is with Shravan Nakshatra and bestows a lots of Punya when kept fast on this day. Taking bath on Sangam (where two rivers meet) gives special fruit on this day. If there is Wednesday and Shravan Nakshatra, then it is good for Daan.
[Agni Puraan, 21]

Sugati Dwaadashee Vrat
On Phaalgun Shukla 12th. Whoever wants to do this Vrat, he should worship Krishn saying "Jaya Krishn Namastubhyam" for 1 year.
[Agni Puraan, 21]

Sumati Dwaadashee Vrat
On Phaalgun Shukla 12th, worship Vishnu.
[Agni Puraan, 21]

Til Dwaadashee Vrat
On Phaalgun Krishn 12th, which is with Shravan Nakshatra. This day one should take bath with sesame water, do Havan with sesame seeds, and offer sesame seeds Laddoo. Light lamp with sesame seed oil, and offer Til to Pitar. Donate sesame seeds to Braahman. One gets fruit of Til Dwaadashee only by doing Hom and keeping fast. Worship Vishnu with "Aum Namo Bhagavatey Vaasudevaaya" Mantra. If somebody keeps this fast like this 6 times, he goes to Swarg with his whole family.
[Agni Puraan, 21]

Til Dwaadashee Vrat
On Maagh Shukla 12th with Aashleshaa or Mool Nakshatra. Worship Krishn with sesame seeds with "Jaya Krishnaaya Namah" and do Havan with sesame seeds.
[Agni Puraan, 21]

Vishok Dwaadashee Vrat
On Aashwin Shukla 12th. Worship Hari on this day.
[Agni Puraan, 21]