First 100 days in a trainee position

Hi David,
There's actually a cast on internship, that actually cover some interesting ground and I'm sure you could be able to get something from this.
http://www.manager-tools.com/2010/04/make-most-your-internship-part-1
http://www.manager-tools.com/2010/04/make-most-your-internship-part-2
Some other key points are: 
Networking - One of the most important - there a number of casts covering this, I have listed a few below:
http://www.manager-tools.com/2006/05/building-a-network
http://www.manager-tools.com/2010/02/intra-company-training-network-building
Linkedin - Specially very valid here, get a profile and connect with some of the people you manage to create relationships with, this is a easy and profession way to stay in contact and also know what they do, where they move to etc, likewise you can get a lot of career history on people which can also be helpful in understanding them.
http://www.manager-tools.com/2010/04/linkedin-managers-part-1
http://www.manager-tools.com/2010/04/linkedin-managers-part-2
Mentor - Personally I got a mentor very early on when I first joined the workplace, at first it was mainly to help me understand more of the job, but at a later stage she was also very helpful in supporting me in my leadership learning.
http://www.manager-tools.com/2006/06/basics-of-mentoring-part-1-of-2
http://www.manager-tools.com/2006/06/basics-of-mentoring-part-2-of-2

Also getting the basic's right with DISC and other basic things like handshakes is important and can make you STAND OUT!
http://www.manager-tools.com/2006/04/secrets-of-a-great-handshake
http://www.manager-tools.com/2006/03/the-d-in-disc
http://www.manager-tools.com/2006/04/the-i-in-disc
http://www.manager-tools.com/2006/05/the-s-in-disc
http://www.manager-tools.com/2006/06/the-c-in-disc
Quite a lot to start with, but alone the fact you are in this forum shows that you want to do well, there's a number of tools in here that can support you very well.
Kind Regards
Mads Sorensen
Disc 4536

Fit in
Don't tell people how to do their jobs
Be interested in other people and their jobs
Learn
Fit in
You are not there to run the company, you are there to learn (hopefully)
Did I mention fit in?