mkdir deb
cd deb
mkdir debian
mkdir sources
cd debian
touch changelog control rules

The last line is important, you need to fill correct data to these files. Rules are simple, changelog is manually filled (needs distribution name, and fixed urgency=low, control can be dummy (FIXME).

Automatically find build dependencies

dpkg-depcheck -b debian/rules build

Build the package

dpkg-buildpackage -S

(In order to upload it, -S option must be given.)

Upload it to repository (e.g. Launchpad).

dput ppa:your-lp-id/ppa <source.changes>