How can I always get Timestamp in certain format without having to explicitly define it everytime
For general preferences you have the DateStyle and LC_TIME settings.

But it would be madness to always truncate fractional seconds automatically - hiding part of the relevant information.

A possible syntax shortcut would be to create a tiny function once:

CREATE OR REPLACE FUNCTION my_ts(timestamp)
  RETURNS text LANGUAGE sql IMMUTABLE AS 
$$SELECT to_char($1, 'MM/DD/YYYY HH12:MI:SS AM')$$;


Then:

SELECT my_ts(entered) FROM analytics WHERE business_id = 371746;