It's often debated just how important fitness is to a cricketer. Context is however required as a fast bowler's fitness levels requirements, a wicketkeeper and an opening batsman to mention but 3 differ greatly.
Cricket requires a multi faceted approach to fitness. Different roles, formats and game situations all have different requirements of the player. From power hitting and death bowling to batting through 50 overs/bowling 20 odd overs in a day. Physical fitness and conditioning must be of a specific nature. Coupled with the specificity, periodisation of the training is essential. For example, heavy weight training has its place, but not during a T20 tournament... All the preparation of course is pointless without the associated development of specific skills.
Breaking down the fitness aspects into simple categories and in turn incorporating them into a periodisation program is key to systematic progression.
A simple breakdown of fitness would be the "6s's":
1) Stamina (endurance)
3) Stability (Core and balance)
4) Suppleness (Flexibility)
Periodisation of the above "s's" could be the following:
Preseason conditioning phase 1:
Stamina, Strength, Stability, Speed (minimal), Suppleness. (Gym). *Divide into dedicated weekly program.
Preseason conditioning phase 2:
Stamina, Strength, Stability, Speed (maximal), Suppleness. (Gym). *Divide into dedicated weekly program. This will benefit recovery period and ensure maximal gains.
Preseason cricket specificity phase 1:
Skills (techniques), Suppleness. (Nets)
Preseason cricket specificity phase 2:
Skills/roles in match scenarios (Nets)
Preseason cricket specificity phase 3:
Warm up matches/analysis/feedback.
This might or might not seem an elaborate plan to prepare for playing cricket depending on your outlook but to quote Benjamin Franklin, FAILURE TO PLAN IS PLANNING TO FAIL!