It is probably a good idea to read some historiography. Examples include -
Richard Evans In Defence of History
EH Carr What is History?
Fernand Braudel On History
Marc Bloch The Historian's Craft
Perhaps also some game-changing books, such as -
Keith Thomas Religion And The Decline of Magic
Fernand Braudel The Mediterranean And The Mediterranean World In The Age Of Philip II
EP Thompson The Making Of The English Working Class
Linda Colley Britons
Niall Ferguson The Pity Of War
Sathnam Sanghera Empireland
The most demanding universities are not interested in hobbies etc, but may be interested in super-curriculars, eg essay competitions, summer schools, and so on.