This question will continually re-appear. Limited permanent storage: so perhaps install onto & run from a USB or flash card instead off the limited space on the PC hardware.
In Australia, most Linux distros install foreign languages, so I tediously remove them. Some install themes, wallpapers, lots of sample files (movies, sounds, pictures, fonts, etc). So - tediously remove these as well.
If you use a 'buntu running LXDE, this helps. When installing, do not allow Internet update whilst installing, because you have little control on the updates it will install.
Netbooks might run Atom (32bit) or I3 processors. Choose 32bit operating systems. If you have more than 3.5 GB of RAM memory on your motherboard, check that your op system is 32bit PAE. 64-bit apps, etc are usually more space demanding.
After the non-Internet install, use the inbuil upddater, or Synaptic to selectively choose what parts you will upgrade. On a small PC, you cannot do everything promised; only a few tasks. So add your preferred apps rather than the ones that have been supplied. Remove the unused apps; perhaps Transmision (torrent), Libreoffice and/or Abiword, etc.
With light usage, you can let 'buntu decide the size of your temporary and other folders, so just let it default install everything into the Root (/) directory.
Most netbooks need or allow wireless netweorks. So your might want to add wireless network apps: signal strength, security, etc. 'Sentinella' and hibernate apps might help as well, since these are rarely installed on most Linux distros, which are designed for desktop-type computers and servers.