There are basically three skills, which are necessarily required to succeed in the interviews.
They are:
1. Aptitude
2. Communication skills
3. Technical skills
4. Attitude/Personality-this is transparent to candidates.
(Candidates can lack one or more skills if they want the job by some shortcut means, but those who want the job fair and square, must possess all the above skills. You know what I mean). Let me consider myself a common man and tell you how I improved my skills. Then you can generalize them better.