The only true karma is that aimed at finding your true self, primarily through meditation or pranayama. Otherwise all karma, be it good or bad, is not good as it traps you in the duality of existence.

That said however, every point of our existence, through inaction or action, we make a choice because we are trapped in a dual existence. The choices available to us are determined by our past karma, but the choice we make will be determined by a combination of past karma (effectively ones samskara or habits) as well as ones' strength and will and desire to defy these habits. In this way new "future" karma will be created.

Dharma is doing ones rightful duty, regardless of ones' self-interest. One's highest dharma is to find oneself, primarily through disciplined meditation. But in our daily existence we are also forced to make material choices which should ideally be dharmic.

Thus when faced with choices, it helps to have a good understanding of ones' dharma so that karma is minimised. But one can only make the "right" choice if one has a detached view of ones' existence, i.e. if one is able to fly high enough to see the complete field of choices and consequences and one is not attached to any results from these choices.

The only way to gain this detached understanding is to meditate. Meditation works on both the material plane as well as the spiritual. Meditation increases ones understanding, thereby improving knowledge of your dharma. This results in right actions which in turn reduce the incidence of bad karma.

A person cannot truly know his/her destiny until he/she is enlightened, at which point of course, the question itself has no value as there is no attachment! Until then, man has to make the best possible judgement. Sciences such as astrology, can help but even then, you still have to make the choices. Are you detached enough to make the right choice on a sustainable basis.
To be detached does not mean that a person can ignore his/her duties. If you are family man, then it is your responsibility to also fulfil your obligations towards your spouse and children. It is to the fruits of your actions that you need to be detached from

Calm Mind