There are many ways in which a pedigree can be displayed, and there is always going to be a balance between the clarity and amount of information you can reasonably display. There's little point in cramming everything onto one A4 sheet if you have to get out a magnifying glass or take a course in cryptology to understand it.
One of the more commonly used and widely understood charts is a fan chart. There is a limit on how many generations you can include on one page, but many genealogy programs have built-in ability to produce such a chart.
There is actually quite an expanse of literature on the subject of maximizing space-efficiency in displaying tree diagrams (much of which is not specific to genealogy pedigree charts). I am sure the mathematics of space optimization are beyond the scope of this question, but if you are interested I would direct you to "Quantifying the Space-Efficiency of 2D Graphical Representations of Trees" (M. J. McGuffin and J.-M. Robert, 2010). There are a number of different types of compact tree diagrams in that paper which you might take inspiration from.
One novel diagram type that I have come across that I think is worthy of a special mention is the fractal-type tree called an H-tree. While not widely used for genealogy, Claurissa Tuttle has described the benefits of her program to produce an H-tree in "PedVis: A Structured, Space-Efficient Technique for Pedigree Visualization" (2010). Her thesis version of this paper can be downloaded here.
An 11-generation H-tree chart would look like the following (image from Tuttle et al.):
It would not be possible to include every ancestor on one A4 sheet, but depending on the number of generations in your tree an H-tree looks like a good option for displaying a large pedigree very compactly. Being unconventional it may require some explaining when you share it with people, but I think after they understand how the H-tree works it is a relatively straightforward means of displaying one's ancestry. Another benefit of this display is it makes it very clear where the gaps in your tree are – all the white space.
As far as I am aware, there are very few utilities publicly available to generate an H-tree from a GEDCOM. As pointed out by @Sam, there is an unsupported add-on in Gramps for an H-tree Pedigree View. Progeny Genealogy also have an option to produce a Fractal Tree Chart. With some effort you could produce an H-tree manually in a graphics program or even in Microsoft Excel.
To keep the tree a manageable size, you might consider breaking it up into pieces – e.g. one chart for each grandparent, or great grandparent. In this way you might be able to fit each part of the tree onto an A4 sheet. And a benefit of this is that when, for example, you share your tree with a relative on your mother's side, you would not have to give them all the information on your father's side too (which they are probably less interested in).
