One of the mistake is ignorance of your catchment area, catchment area are the geographical area served by an institution. Every University, Polytechnic or college of education has a catchment area it primarily serves. This does not mean that schools will not admit persons outside their catchment areas, but catchment areas are given special considerations.  Example Lagos state University (LASU) gives special considerations to student from the six south western states. This is done by giving applicants from this state a lower cut off mark. 

Schools also have special requirements for different courses, for example further math in WAEC, is required in UNILAG for Engineering courses. Therefore you can have all A's in WAEC, 300+ in JAMB UTME, but will not gain admission because of you did not write Further Math  in SSCE.  

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