Bill, the galactic hero - Harry Harrison

Bill was a peaceful farm boy until he was lured by the martial music of a
passing recruitment sergeant, drugged, and made to enlist in the Empire
Space Corps. His basic training is sheer hell, but somehow he manages to stay alive and achieve the rank of Fusetender 6th Class in the process.
En route to an engagement with the lizard-like Chingers, Bill's
spaceship is involved in a supreme conflict and -- by accident -- Bill is
the man who saves the ship and wins the day. A grateful Galaxy awards him its highest accolade: the Purple Dart, to be presented by the Emperor himself on the fabulous aluminium-covered planet Helio. And then his adventures really start to take off in the most bizarre and surprising ways . . .