What we have to do for bad karma from a prior life?

We live in a befuddled world where one is born inferior and another superior. The inequalities among each other are numerous. How could one be born into a life of affluence, and another to abject poverty? How could one live long and another die young? How ill-luck could befalls the virtuous, and the wicked have all the luck? Why would one have to lead a sickly life when another is strong and healthy? How can there be a ravishing beauty and an ugly duckling in the same family. It is these kind of observations that made you ask the question… If our present suffering is the result of bad karma from a prior life, what is the real present remedy for suffering in this life?

This is where the Buddha’s teachings come in help. The teaching on kamma, or intentional action, is perceived by most of us as the idea that what you experience now comes from what you did in the past. It is erroneous thinking. What Budddha said was:

“Chēthanāhan Bhikkhavē kamman vadāmi. Chēthayithvā kamman karōthi kāyēna vāchāya manasā”

“Dear Bhikkhu, I see intention as the Kamma. One does Kamma by body, words, and mind based on an intention.”

Nibbēdhika Sutta http://www.accesstoinsight.org/tipitaka/an/an06/an06.063.than.html

The subject of outcomes of Karma is infinite. Only a Buddha has the ability to understand it. Buddha has said that our experience of the present moment consists of three things: pleasures and pains resulting from past intentions, present intentions, and pleasures and pains, resulting from present intentions. This tells us that the present is not totally shaped by the past. Pleasures and pains come from intentions, which are actions. So in a sense, it means the meritorious and de-meritorious volition (Kusala Akusala Cetana) or in other words "action-influence.".

Buddhism does not assert that everything is due to Kamma. If it is so, a man must ever be bad, for it is his Kamma to be bad. But as per Dhamma, there are five orders or processes (Niyamas) which operate in the physical and mental realms:

Kamma Niyama, order of act and result, e.g., desirable and undesirable acts produce corresponding good and bad results.

Utu Niyama, physical (inorganic) order, e.g., seasonal phenomena of winds and rains.

Bija Niyama, order of germs or seeds (physical organic order); e.g., rice produced from rice-seed, sugary taste from sugar cane or honey etc. The scientific theory of cells and genes and the physical similarity of twins may be ascribed to this order.

Citta Niyama, order of mind or psychic law, e.g., processes of consciousness (Citta vithi), power of mind etc.

Dhamma Niyama, order of the norm, e.g., the natural phenomena occurring at the advent of a Boddhisatta in his last birth, gravitation, etc.

Every mental or physical phenomenon could be explained by these all-embracing five orders or processes which are laws in themselves. Kamma is, therefore, only one of the five orders that prevail in the universe.

your question falls into the 6th thing Buddha said we should know about Karma

1) what is Karma - intention

2) stage where karma is played out. (i dont know if my pali English text is correct, Nidhana-sam-Bhava) the answer is Pasa or dection. Karma can bare result in those who have detection. This matches independent origination detection is a condition for feeling to arise, in this case feeling of unpleasantness.

3) levels of Karma; karma that results in beings to be in hell realms, in animal wombs, in hungry ghost realms, in human realms, in heavens.

4)Time of karma. Immediate, further in the future, or even more further in the future.

5) the end of karma. Karma ends when detection ends.

6)path/road to the end of karma. That's 8 fold paths.

Please notice that the fundamental things to know about Karma matches well with OidaOudenEidos' answer. Right mindfulness and concentration are 8 fold path.

This Demonstrates Buddha's great ability, no matter when and where he spoke of Dhamma, they all match well together.