Here is the thread on the 1/35 Tiger I recently completed. This was the first time I had added some damage and shell hits. I took the head of a small nail and heated it up a bit. I then pushed it into the plastic and gave it a bit of a twist.
The smaller holes on the exhaust covers were done the same way, but with the pointed end.
I just looked at some nice Tiger 1 battle vets and used my imagination! Good luck and have fun with it!
http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=6132&whichpage=1