What is tapas?
The word tapas means austerity. What constitutes austerity? Any act of self-discipline, ranging from controlling senses to controlling the Mind all of this is tapas.
Sri Swami Sivananda says in Raja Yoga by Sri Swami Sivananda that all kind of spiritual disciplines come under tapas.
Tapas is austerity. Egolessness and selfless service are the greatest forms of Tapas. Humility and desirelessness are the greatest forms of austerity. Practice these through ceaseless, untiring, selfless service. Practice the three kinds of Tapas mentioned in the Gita. Disciplinary practices like fasting, etc., also come under Tapas.
Do all forms of meditation come under tapas and result in punya?
Meditation can mean sitting in an asan, and praying to God, repeating God's name, or it could also mean being absorbed in yourself.
Sri Krishna says in the Gita 6:12
Sitting and concentrating the mind on a single object, controlling the thoughts and the activities of the senses, let the yogi practice meditation for self-purification.
So Sri Krishna says that meditation yields self-purification.
In Patanjali Yoga Aphorisms, Chapter III, verse 2:
The mind tries to think of one object, to hold itself to one particular spot, as the top of the head, the heart, etc., and if the mind succeeds in receiving the sensations only through that part of the body, and through no other part, that would be Dharana, and when the mind succeeds in keeping itself in that state for some time, it is called Dhyana (mediation).
Thus in the advanced stages of Meditation is the state where one goes above punya and papa. That is He is absorbed in Himself, thus neither punya nor papa can touch Him.
Sri Krishna says in Gita 6:20-22
When the mind disciplined by the practice of meditation becomes steady, One becomes content in the Self by beholding Him With (purified) intellect.
One feels infinite bliss that is perceivable only through the intellect, and is beyond the reach of the senses. After realizing Brahman, One is never separated from absolute reality.
After Self-Realization, One does not regard any other gain superior to Self-Realization. Established in Self-Realization, One is not moved even by the greatest calamity.
Basically upon reaching the final stages of meditation, the question of punya and papa will not occur and nothing will be able to affect the One.
What advice would you give to a meditation beginner who wants to do it as per Hindu tradition?
Sri Swami Sivananda in 'Guru-Bhakti Yoga':
A Guru is necessary for every aspirant in the spiritual path.
It is only a Guru who will be able to unveil the mystery and meaning of real life and show the way to God-realisation.
Guru will be able to awaken the hidden divine power in the innermost core of disciple’s heart.
Without the help of Guru one cannot attain the knowledge of the Self.
Meditation on Guru is the pathway to Divinity. It is the royal road to Kingdom of Brahman.
So basically that the highly complicated techniques may or may not lead to self-realization. But following the path of the Guru is the sure way. In other words, all the meditation etc that is done is only to get the grace of God.
So whatever meditation technique is followed, please be sincere and steadfast, then Guru's grace will surely follow. All the best sir!!