I use the k&r indentation style, but with the slight modification of keeping braces on the same line as functions as well. Try to keep to this style as much as possible. If you've written some code in a different style, you can re-indent the all of the C files with
make indent
as long as you have the command-line utility indent installed on your system.
I don't really follow any guidelines for NASM, other than the ones which the emacs assembly mode enforce. I don't mind which style you use for this.
Any contributions are welcomed, of course - being an open source project.