What are results of doing good Karma?
Yudhishtira wanted to know this from Bhishmacharya.
This was Bhishmacharya's answer.

You get results of your karma in the next births depending on how you have done it.
If you have helped somebody with your body, then you will see comforts coming to your body,
If you have done good karma with your words, like you have acquired punya by chanting Vishnu Sahasranama, then you will hear good words and praises in the next birth.
For good mental karma, you will get mental happiness, peace in the subsequent births as a result of that.
It also depends on when you have done that particular karma.
If it is during your youth, then the result also will be in the youth.
If it is during old age, then the result also will be experinced during old age.

How and when of your karma are important.
Dedicating both your body and mind in doing good karma is very important.
For example, if an atithi comes to your place -
Welcome him with pleasing eyes, talk to him sweetly, serve him with eagerness, don't allow yourself to be distracted by phone calls or something else, as long as he is with you, spend your entire time exclusively for him.
When he leaves, accompany him upto some distance.
If you serve an atithi with such dedication, you will get the results of doing a yaga.
See, how important is hosptality in our cullture.
Atithidevo bhava - treat your guest as if he is God, he should be like God for you.
In the hospitality Industry, customer is king, guest is king.
In our culture, the guest is God.

Someone who comes to your place hungry and thirsty, he should not be ignored even if he is a stranger.
Those who give up a comfortable bed and sleep on the floor, they get comfortable bed throughout their next birth.
That is the principle of sacrifice.
It is like saving for the future.
Give up now, get it later.
Whatever is due to you has to come to you some time or the other.
If you give up now, it will come back to you later.
If you give up expensive clothes and adopt simple dress, then you will never be short of good clothing in the future.

If you overcome duality - that this is good and that is bad, he is good and the other one is evil - this is the goal of yoga - then you will get comfortable vehicles in the future births.
This is the result but whether it would really matter to you after having achieved a state of non-duality is a different question.
If you worship Agni in this birth, then you will be reborn with a lot of courage, strength, and valor.
If you give up craving for tasty food, then you will get sowbhagya in the next birth.
If you give up eating non veg, you will get wealth and progeny.
Observing intense yogic practices and brahmacharya will make you achieve all your desires in the next birth.