After installing lubuntu 14.04 you need to add "Canonical Partners" on the repository settings, otherwise you can't install some important software on lubuntu.
For example if you try to install skype using apt-get install command, you will get error message saying that "E: Unable to locate package skype".
To solve this problem, open Synaptic Package Manager (start menu > System Tools > Synaptic Package Manager).
On Synaptic Package Manager select Settings > Repositories > Other Software, make sure the "Canonical Partners" options are checked, like this :
And then hit "close", you will be prompted that the repositories are changed, hit "reload".
It will start to download the package information from the internet, so make sure the internet works.
Now you should be able to install popular software that's part of "Canonical Partners" such as flash, skype, java, open ssh server, etc.