Physical conditioning is an important part of training.  I recommend training for strength, speed, and endurance.  Regular weightlifting and body-weight exercises are good, as well as running, swimming, and cycling.  For running I recommend both long, slow distance runs as well as interval runs (e.g. spring 100 yards, rest, then repeat 5 to 10 times).  For a beginning athlete, I recommend the following schedule to get started with running.  This is almost the same schedule that Naval Special Warfare recommends aspiring SEALs follow to prepare for the rigors of BUDS (Basic Underwater Demolition/SEAL training).

Week 1

Run 1 mile each day, rest on the weekend

Week 2

Run 2 miles each day, rest on the weekend

Week 3

REST.  Your body needs time to acclimate to the stresses that running puts on your legs and your joints.  Cycle, swim, lift weights, do body-weight exercises, but DO NOT run during week 3.

Week 4 and beyond

Continue running 2 miles each day.  Work on improving your speed.  Also, every two or three weeks you can increase the distance of each run by 1 mile.  If and when you get up to 9 mile distance runs, that is probably as much as you really need.  My own distance runs are usually only 2 or 3 miles depending on how much time I have available to train.

Below is the training schedule that I follow myself

Monday, Wednesday - lift weights (incline press, shoulder press, abdominal crunch, lat pull, leg press, calf extensions), swim

Friday - body-weight exercises (squats, push-ups, sit-ups, pull-ups), swim

Tuesday, Thursday, Saturday - commando combatives, distance running, striking conditioning

Sunday - yoga, practice commando combatives with a partner, sprints (100 yards x 5)