Is it possible to lay a block adjacent to another without looking at the face of the existing block?

If you sneak SHIFT you don't have to be so careful since you don't fall while sneaking.

If you are putting down that is level just snaek and walk backwards constantly and place your blocks.

A trick to get you stay in sneak mode (on Windows) is to press SHIFT down then press and release ALT release your SHIFT key and click back into the game with your mouse. You should stay in sneak mode untill you press SHIFT again, meaning you can move around without falling off any ledges.

http://www.minecraftwiki.net/wiki/Sneaking

In Windows, you can enable sticky keys by pressing Shift 5 times in a row and clicking Yes. Then press shift twice; it will stay in sneak mode until you push shift again.