Adcoms like to see shadowing in the primary care field... I found asking my personal physician to be the best for this. Also, if you shadow your family physician/pediatrician they might be able to give you names of other doctors in certain fields you think you might be interested in.
The other thing that worked for me was asking friends/family if they knew doctors. I found a random connection in the field I wanted to pursue. That connection set me up with herself and other doctors in the department for about 10 days of shadowing in all the different divisions of that specialty (Peds Hem/Onc so I did days with neuro-onc, sickle cell, hemophilia, solid tumors, bmt, etc)
Many have said it is beneficially to volunteer in a hospital and meet people there- I volunteered for 3+ years but the area I was in didn't have physician interaction (but I loved what I did).