Lennart was speaking at the Technical University of Berlin about "things you need to know, things you should expect and things you shouldn't expect when your are aspiring to become a successful Free Software Hacker."
Lennart has now published the slides on the Internet, which are aimed for university students and others aspiring towards contributing to Linux / open-source software.
The slides are embedded below or they can also be viewed from this link on Google Docs.
Among his points are starting with patches, "scratching your own itches", reading sources and learning to use Git, learning all the proper development and build tools, be enthusiastic and persistent and dedicated, make your code attractive, etc.
If you're interested in this topic, you will also want to see my Q&A panel from last month at XDC2011 Chicago that was with several key X.Org / Linux graphics developers about contributing to open-source projects. Many of the people on the panel began contributing to Mesa / X.Org while at university and have since been hired off by the major Linux players, etc.