Build body strength. If you aren't already on a workout program, get on one. The sooner the better. CARDIO, CARDIO, CARDIO!!! Your endurance, stamina, and strength are all pushed to the max during emergencies....
Besides fitness,never expect a call to go like the book says it should. Expect the unexpected,emergency scenes are dynamic,ever-changing. Take advantage of every call to learn,what went right, what can you improve on?
Don't expect to come out of the training academy as an expert-your learning curve should never end.
Fitness is important but more important is practice safety and keep your eyes open on a scene and soak it all in.Like has already been mentioned what you read in a book and what actually happens are two totally different things.Like an old timer from my department told me when I got on and I live by these words "when you think you know it all,it's time to retire because your gonna get your self hurt or killed!!"