Nowadays it is very difficult for almost everyone to have full faith in god and scriptures(Vedas, Ithihas, Puranas, etc). In what ways a person can increase faith in the above mentioned things?
Having faith in gods and scriptures is collectively known as Astikya (the state of being an Astika as opposed to a Nastika).
Now we know that Yoga has the eight limbs (Angas) among which we have Yama, Niyama etc.
And, in that list of limbs, this Astikya comes under Niyama.
See the following verses from Devi Bhagavatam (Book 7 , Chapter 35):
The enemies to this Yoga are six; and they are lust, anger, greed, ignorance, vanity and jealousy. The Yogis attain the Yoga when they become able to destroy these six enemies by practising the accompaniments to Yoga. Yama, Niyama, Âsana, Prânâyâma, Pratyâhâra, Dhâranâ, Dhyâna, and Samâdhi, these are the eight limbs of Yoga. Yama includes Ahimsâ (noninjuring; non- killing); truthfulness; Asteyam (non-stealing by mind or deed); Brahmacharya (continence); Dayâ (mercy to all beings); Uprightness; forgiveness, steadiness; eating frugally, restrictedly and cleanliness (external and internal). These are ten in number. Niyama includes also ten qualities :-- (1) Tapasyâ (austerities and penances); (2) contentment; (3) Âstikya (faith in the God and the Vedas, Devas, Dharma and Adharma); (4) Charity (in good causes); worship of God; hearing the Siddhântas (established sayings) of the Vedas; Hrî or modesty (not to do any irreligious or blameable acts); S'raddhâ (faith to go do good works that are sanctioned); (9) Japam (uttering silently the mantrams, Gâyatrîs or sayings of Purânas) and (10) Homam (offering oblations daily to the Sacred Fire). There are five kinds of Asanas (Postures) that are commendable: Padmâsan, Svastikâsan, Bhadrâsan, Vajrâsan and Vîrâsan.
Now, Yama in the list precedes Niyama. So, this implies that to be established in the qualities of Niyama (of which Astikya is a part), one first needs to master the traits of Yama.
Basically, the reason for not having Astikya is previous birth sin. And, to destroy those sins we need the disciplinary acts of Yama.
So, in other words, by following non-injury to beings, truthfulness, non-stealing, a merciful attitude, cleanliness, a regulated eating habbit etc (the whole list of qualities of Yama is already found in the quote above) one can gradually attain faith in gods and scriptures if one is lacking in that department.
Also the Devi Bhagavata Book 7, Chapter 39 states that by following a Dharmic lifestyle one can increase Shraddha/Bhakti. So, following Dharma is the key for those who are lacking in faith.
O King of mountains! Meditation with Karma and Jñâna with Bhakti will lead one to Me. Only the work alone will fail to get one to Me. O Himavan! From Dharma arises Bhakti and from Bhakti arises the Highest Jñâna. What are said in the S'ruti and Smriti S'astras the Maharsis take that as the Dharma; and what are written in other S'astras,