How can one get good marks in engineering services exam's conventional paper?

For acquiring maximum possible marks ( 70-80% of indicated marks)  in a question you may follow some basic rules

• Write all the given data with unit indicated.
• Write all the assumptions related to The theory or concept on which the answer is based.
• While solving numerical always indicate the formula you ve applied.
• If possible give the line diagram for numerical.
• While writing theory questions draw the diagram without any criss crosses. Use proper scale . no rough. Its ESE not semester.
• Use black or green pens along with blue . it creates good impression.
• Underline important fact in the answer.
• Always write the unit of answer you get. Mandatory!! 
• Write the answers, step by step in tidy manner to give an impressive presentation and by doing this the candidate will not miss the essential points and formulae. If some diagram is required try to make well labelled and neat diagram with freehand sketch. You will get the credit for orderly, effective, and exact expression combined with due economy of words in the conventional papers of the examination.
• Write formulae in the numerical, S.I units of concerned quantities and answers as well. Steps to enhance your performance:-

Remember these steps can only be taken if you've practiced a hell lot of time. So that's most important to develop a habit in same manner while preparation.

ESE is all about choosing the best candidate among all. So make sure give your best.
Good luck !!