Adhik-Maas or Purushottam Maas is the extra Lunar month that occurs every 3 years 3 months and this month is considered to be very auspicious and dear to Lord Krishna.
During this Purusottama mass devotees perform following austerities/activities
1) Chant more numbers of rounds than regular days. 18-24-32-48-64 etc
2) Complete your fix chanting rounds in Brahmamuhurta (Before 7am.)
3) Sleep on floor (with proper bedding).
4) Get up before sunrise and take bath.
5) Attend as many as mangala arati in temple.
6) Follow celibacy (Brahmacharya) for month.
7) Offer ghee lamp to Lord 1 or 2 times in day and sing/hear Brahma Samita.
8) Read and Meditate on Bala-Lila from Krishna book, Bhagavad Gita and Srimad Bhagavatam.
9) Do minimum 1 or 3 parikarama of temple daily/whenever you visit Temple and/or minimum 1 parikrama to pilgrimage once during vrata.
10) Visit Dham and take bath in Holy Kunda or River.
11) Eat regular meal but ones in day, afternoon time or evening time. (Health should not be compromise on the name of austerity.)
12) Avoid oil in food. Use ghee.
13) Give donation to temple as per your capacity.
14) Do some fix service/seva in temple as per your capacity/capability.