http://developer.ubuntu.com/packaging/html/packaging-new-software.html
-or-
Summary
Prerequisites
Get the new tar
Ensure it follows the right name pattern
apt-get source to get the current package
Copy over the debian/ directory
dch for a new changelog
debuild to build it

Prerequisites
For general building:
sudo apt-get install build-essential kdelibs5-dev git-core cmake 
For build dependencies (in this case for rekonq):
sudo apt-get build-dep rekonq

Get the new tar
In this case, from http://sourceforge.net/projects/rekonq/files/1.0/rekonq-1.3.tar.bz2/download?use_mirror=iweb

Ensure it follows the right name pattern
In this case, use Dolphin rename to rekonq_1.3.orig.tar.bz2

apt-get source to get the current package
In this case apt-get source rekonq

Copy over the debian/ directory
In this case use Dolphin to copy the debian folder from 1.1 over to 1.3

Add a new changelog entry for 1.3
In this case:
cd rekonq-1.3
cd debian
dch

debuild from the new directory to create the package build