Software design principles

Can anyone recommend some good books, web sites or courses on software design principles that are sufficiently generic to be used with PBP projects?

I am self taught in BASIC and am fairly handy with PBP in small systems but there must be some good overall principles that will improve my code and get me finished sooner. My current project has 4 PIC18F4620 and two PIC16F88 all chattering amongst themselves and the entire project is out of control.

All help gratefully received.

Cheers
BrianT