One of Shiva's names is Someshvara (the one who put the Month / Moon (Soma) in his hair).
The moon, in turn, is the ruler of Monday. Therefore, Pradosh, which falls on Monday, is considered one of the most favorable for Shiva's rituals.
Among other things, observing fasting on Mondays helps to balance the negative manifestations of the Moon in the horoscope (removes Chandra dosha).
It is believed that those who are fasting at this time receive the favor of Shiva (who gave the teachings of yoga to humanity) and his wife Parvati (as well as his entire family and tamed animals), and he (all of them 
) contribute to deepening knowledge and strengthening the effect of yogic and tantric practices and rituals.
Yogis observing this fast can achieve Moksha (enlightenment, liberation from the burden of subsequent rebirths) and receive forgiveness for their transgressions and atonement for sins.
Also, some scriptures say that on this lunar day Shiva cleans the Earth and people from negative karma.
"Pradosh" means getting rid of the dosha (dosha = problem / defect acquired as a result of sinful actions in the past).
The most significant Pradosh fast is considered Mahapradosh, preceding Shivaratri (in February-March), as well as Shani Pradosh, Soma Pradosh and Bhumi Pradosh. Fasts these days will lead to more serious transformations.
How to fast in Shiva Pradosh:
On this day, complete abstinence from food is recommended, only juices and water are allowed.
If, for some reason, it is impossible to completely abstain from food, then it is allowed to eat raw fruits and vegetables.
One should leave the fast after the onset of the next lunar day (chaturdashi).
Recommended rituals in Prados:
- Shiva Puja,
- gifts for Shiva (honey, milk, Ganges water, rice, fruits),
- reading and listening to Shiva's mantras,
- visiting temples of Shiva,
- lighting incense and / or candles,
- worship of Shivalingam or Shiva statues.
