Can anyone remember how you move your units so that they stay in formation, ie. I have line infantry in front and other units set out behind and I want to move them forward, the game just puts them in one long line and I have to micro manage!

Without knowing the specific TW game and not being at a computer with a TW game to check, I believe the unit formation button is at the bottom of the screen in the User Interface. I think there's a button next to the time compression.

Select the units, GROUP THEM, then move.

Or use the arrows on the bottom left. They let you move formations in place, and turn them.

I've never used the arrows! lol, I'll go and try now.

Also, how do you group? I was pressing CTRL+G but did nothing.

There should be a big button for groups, on the interface. Which TW gives you trouble?

I'm playing Shogun 2 ATM. The arrows are working great though.

highlight the units you want to group and press the g key to group them. to remove a unit from that group highlight its card and push g again to de-group that unit. you can use ctrl-click to select more than 1 unit. each group will have a small number above the unit cards, push the corresponding number key (keyboard top row) to quickly select that group. if you have a group set up in formation, clicking and dragging the right mouse button will order them to move to a new location but keep the same formation. i find that if i accidentally select an extra unit that isnt in the group it messes up the formation and dragging right mouse only forms them into a line as you described previously, this also happens if i click and drag with the left mouse button and miss a unit out of the formation by accident.

i find the key is to set up all your units in a nice formation during the pre-battle phase, then use right click and drag to move each group.

Try out the cool formations that pop out on the arrow to the left too. I like to advance in Bark of the Tree...

Mouse grabbing units and hitting CTRL 1-9 will creat a group with that number as well, just hit the number and gain the group.

I find that they some times attack strangely if I have them in a formation and tell them to attack. Usually that's the situation where I am thinking... "Forget all that, Loose bows, Charge, now!!!" and they try to maintain their weird idea of how I want them...

Yep, it's Cntrl + a number ( 1-9) while the units you want are highlighted.

They will stay in their position relative to eachother, so you need to position them, highlight them, hit cntrl 1-9.

Also you need to un-group them if you want to split them or rearrange the layout. I think that's - number(1-9) then G