How to rebuild Ubuntu package from the sources

There are two ways (at least) to rebuild Ubuntu package from the source.
Using Ubuntu diff file and dpkg-buildpackage

• Download source from Ubuntu repository.
• Download Ubuntu diff file and apply it:
  patch -p1 < ubuntu.diff
• Build package:
  dpkg-buildpackage -rfakeroot

Using .dsc file and debuild

• Download .dsc file
• Run following command:
  dpkg-source -x file.dsc
  Note, sometimes the archive with sources should be presented in the same directory!
• Go to source directory and start building:
  debuild

In both cases the development packages should be installed first:
sudo apt-get install build-essential devscripts