A honeycomb grid on your flash helps direct and concentrate light, and depending on the design of the honeycomb you can even achieve a very tight spotlight. YouTube member CAMPHOTOPIX shares his DIY grid build that is based on a bunch of cut straws. I'm not sure where this first started from, but it's an old DIY build that even I have tried years ago. It's very effective and you can customize the length of the straws for different effects. I also like his use of neoprene material for a very snug fit.
These grids were very expensive a few years ago, but if you lack the patience, you can now find similar style honeycomb grids for less than $13.00 dollars shipped. You can find them in 1/8" and 1/4" honeycombs on eBay (click here).
Honeycomb Flash Grid Speedlite