The money I earn overnight goes to my offense all day. I'll load up as best I can in the morning, grab some early cash and keep on buying new offensive crap.
In the afternoon (if I have enough) I'll sell all my offense and get the next siege technology. Again, building my offense throughout the day.
When night comes (or whenever I 'stop for the day'), I'll sell all my offense and put EVERYTHING into defense to try and make it through the night (plus selling all my offense will drop my ranking dramatically, so I -will- be able to survive the evening).
This 'new defensive items' don't get put back into O... instead when I get enough it'll go into the next type of fortification.
The key is... as soon as rankings come out, buy offense and attack people that 'should be' around your ranking. Since they are so much lower than you, you should get mad cash. Then at night, you drop all your offense (and push yourself way too high in the rankings), so it'll be easier to defend the 'overnight raiders.'