I am lazy, so I will only give one.
You can set multiple waypoints (movement commands) for a unit by holding "shift" and clicking points with your mouse. I think I got it to work with going past a unit and then attacking from behind. I don't think the attack command works with hold shift + mouse click all the time--I am not sure.
I also knew that worked in Empire, but I forgot all about it in Rome II until the 40th hour.
Oh okay, so I lied tip 2.
The unit formations are also pretty useful. I'm not talking about single unit formations, those are useful too--I am talking about the formations menu for multiple units. I thought I had to pick a large amount of units to get those formations to work, but they work excellently with just 2 units. They are useful if you want to make 2 units walk in a column or if you want to have units walking on a slant in a perfect row.