Always design your system with debug in mind!

provide a few spare pins that you can watch on a scope, or attach a few LEDs; have the software write easily recognisable patterns to this at key points.

if your chip has JTAG debug, provide access to it! For production, you could just not fit the actual connector - but keep the access there.

have the facility to write debug "trace" messages to a serial port.

set aside some memory for statistics recording, post-mortem info, etc - and provide a means to access it!

One Client had a policy that 10% of system resources should be set aside for debug assistance.


As Michael always says, when starting a new project, always start simple:
Start by just flashing a few LEDs, or writing "Hello, World!" to the serial port;
Add functionality incementally - don't write masses of software and then dump the whole lot onto the target all at once!


Use a Simulator to test software before it reaches the hardware (this will be more beneficial to some parts of your software than others).



Consider how you will test software as you write it.