How can I add additional detail to large walls? I've seen some rather impressive castle builds over the years, and with the release of Helm's Deep I'm clearly going to be building a few myself now.

As this set uses the LEGO sticker sheet to add some detail to otherwise flat walls, I'd like to modify these builds to include some better "brick based" details - but I'm not sure where to start.

Ideally I'd like to create some additional depth, and perhaps add some vines or ivy up the walls, that sort of thing.

Unlike previous questions I have a fair selection of bricks, including various SNOT elements.
Classic-Castle.com has a guide for making castle walls more visually appealing. Key points:


Different colours, shades and textures of bricks add subtle imperfections.
Break up the monotony with windows, doors, arrow slits, balconies and other structural features.
Use timber (brown/tan) as well as stone (grey) bricks and try out adding different materials.