1) `pull-lp-source <srcpkg>` [from ubuntu-dev-tools]
2) cd <srcpkg>-<version> [tab complete can help you figure it out]
3) For each change you want to make to the package: make changes to the package contents
  3a) If you are making changes to the upstream, they will end up (for most packages) as quilt patches in debian/patches
    3a1) After changing the upstream source in the package, run `dpkg-source --commit` [from dpkg-dev]
    3a2) This will prompt you for a quilt patch name, specify it as desired (usually descriptive of the fix)
    3a2) This will then open EDITOR on it
    3a3) That quilt patch file will contain some comments and default headers. Edit them according to DEP3 (http://dep.debian.net/deps/dep3/)
        3a3a) This provides details about the patches contents like upstream source, patch author, etc.
    3a4) It also helps at this point to review the patch and ensure it looks good/as expected in EDITOR
    3a5) Save and quit EDITOR
    3a6) Run `dep3changelog debian/patches/<patchname>` [from devscripts]
    3a7) Run `dch --edit` to clean up the changelog entry [from devscripts]
        3a7a) You can either pass -R to `dch` to specify the release or in the --edit, change UNRELEASED to the appropriate release target (e.g., artful for the development series)
  3b) If you are making packaging changes (changes to debian/ itself), they will not be quilt patches.
    3b1) Document the changes in this iteration of 3) with a `dch -i` (if this is the first change) or `dch --edit` (if this is the second or later change)
        3b1a) You can either pass -R to `dch` to specify the release or in the --edit, change UNRELEASED to the appropriate release target (e.g., artful for the development series)
4) Changelog versioning can be tricky, and for development releases, generally, `dch` will do the right thing. But verify it is the correct version following https://wiki.ubuntu.com/SecurityTeam/UpdatePreparation#Update_the_packaging especially for SRU (fixes for released versions).
5) If this is the first Ubuntu delta for a package (meaning it was direct from Debian before), run `update-maintainer` [from ubuntu-dev-tools]
6) Run `dpkg-buildpackage -S -nc -d -uc -us` which builds a new source package with your changes, without running clean, ignore build-depends and not signing the resulting .dsc and .changes files
  6a) The resulting .dsc file is in ..
7) A 'debdiff' is the result of running `debdiff <olddsc> <newdsc>`
  7a) You will generate such a debdiff, save it to an appropriately named file and attach it to the bug.
  7b) Subscribe ~ubuntu-sponsors to ask for it to be uploaded/sponsored.