The answer varies from the younger ones to grown ups.

Coming to the younger ones; i personally am of the opine that the key essentials to keep in mind before deciding upon any career are as follows:

1. Inquisitiveness of the child = What depth of inquisitiveness does the child have. (I personally believe that every one is born with a certain inquisitiveness level which as we grow up tends to vary depending on various conditions and situations)
2. Passion Level = How passionate the child is towards anything or everything. (Being passionate or showing passion towards something or some one during the childhood is natural. so understanding this passion level makes us to think of his abilities and capabilities the child is willing to develop)
3. Equilibroception (Sense of Balance) = This is that which grows along with the child; which i feel personally another important factor both “Physically and Mentally.” Understanding a child’s sense of balancing level and then making the child to understand his/her Equilibroception and there by nurturing it to grow further enhances the chances of his being in his suitable career. Therefore i conclude for the above that for a child i personally feel that these 3 factors become essential (P. I. E.)

Coming to the aspect of a grownup (19 years and above) there are 3 essentials to consider

1. Combination = Finding the right opportunities at right situations and being in the aspect of taking deviations as and when required but never being away from the main goal. (In a sense, is more like doing SWOT Analysis)
2. Coordination = Utilising to the optimum level of the inner strength to the availability of the opportunities. (I personally feel that many aspects come our way to stop us from chasing our dream career; but this coordination is what helps us to maintain the balance and make a career of our choice.)
3. Culmination = This is the final act that decides whether we will be making to our career or not.

Therefore i personally believe that these are the essentials to keep in mind before deciding any career.