Good luck and have some fun. I have always wanted to do a decatholon. I was a good distance runner and a good sprinter as well as performing well in all feild events. The discus is a very fun event and alot of it has to do with balance and hip explosion. Have someone teach you the proper technique more importantly someone who is small for thier throw, many of the bigger throwers can power through the spin and basically chuck the disc as far as thier strength will let them.
Much like getting perfect timing on a golf swing, leverage and timing along with power at the right point is really what makes a throw go well.
Shotput on the other hand, is more about raw power, this is probably the one event that I myself would not fare well in, but heck, if I can win the other 9 who cares right
On the polevault, be sure to stay aggressive while learning to vault. Also, some mats placed in front of the pit is a good idea for begginers as many tend to fall back towards the runway.
Also, NEVER let go of the pole, unless it is to complete your release over the bar. I had a bad experience once while learning, I was not aggressive enough on my approach and stalled almost straight up and down with my feet driving up in the air. When my body started coming back down and the pole stopped moving foward, I kind of just let go of the pole and fell about 10 ft back into the pit and landed on the back of my shoulders and back of my head. This was not a fun experience and it took me a long time to get over the fear of it happening again.