DrAzzy:
Use a ground pour, not traces for ground - this makes a better ground, and greatly eases routing. Use the polygon tool to draw the outline of the pour (eagle will handle clearance from holes, traces, and board edges), and then click one of the edges with the name tool and change it to the name of your ground net (which you should name GND, but probably haven't because you say this is your first PCB)Where is power coming in? How is it supplied? Be particularly careful when powering something from automotive 12v supply, as the voltage on it can be significantly higher than 12v when the battery is fully charged, and it is notoriously noisy, with large spikes.
Thanks, I started off using ground traces (the ones you see) and then had the major "DOH" moment and did a ground fill for the remaining half. Didn't include that in the picture though since it makes everything else hard to see. I should really go back and remove the first half of ground traces and do it all with the pour like you said though.
Input power will be coming from the vehicle, but it fed to the recom r-78E9.0-0.5 for constant 9v to the nano and then branches off 5v/3.3v from there. This setup hasn't appeared to have any power spike issues on the prototype breadboard versions (probably just jinxed myself).