There is a lot of stuff out there about this, but none of them worked for me as well as this. The difference is that the deborphan command pretty much just lists the packages you actually installed, not the stuff that got installed as a dependency.
On your old machine:
apt-get install deborphan
(Edit: parameters were backwards)
deborphan -a --no-show-section > installedpackages
copy the installedpackages file to new machine
you might want to check your ppa’s and sources.list if the next commands show missing packages.
On your new machine
aptitude install $(cat installedpackages)