I don't have too much experience playing this game, but I start most of my attacks when I get my infantry, or rifles at least. I feel safer with the tech advantage. This usually leads to tanks, and totally dominating the battle field.
After reading a lot of comments on these forums about attacking early, and how if you plan for a military victory, you should never get to the stage where you can get tanks. I decided to try to "rush", and engage an early war campaign.
What I've found is that... without the tech advantage, my units just get slaughtered !! I had axemen against Skirmishers and a force of more than 4:1. Cost me the entire stack to just kill 3 units.
I've just started playing on noble, and the combat odds seem so biased towards the computer. Unless I've got a large advantage, then the computer always seems to fkn win ><