Couple of other points.

1) If you are not sure that your army is going whewre you want it to go, try pressing down the spacebar. This normally displays markers showing the destination of your unit(s).

2) As a general principle if you select more than one unit (or all of them) then they will move where you tell them to but retain the relative position they held to each other when selected. This can actually be a problem if you don't want them to, but it sounds like you do.

CTRL+M will select all missile troops.
CTRL+C will select all cavalry (including elephants etc)
CTRL+H all hand-to-hand troops.
CTRL+[Unit] All units of that type.
CTRL+A all the Army

These are the way I normally control my army rather than using groups which can cause problems.

Clicking the shield symbol can also be useful as it tells a unit to defend its current location. I find this useful with skirmishers as if they get driven off by the enemy they normally wander back later and resume their original position. Which avoids a lot of phaffing about collecting them.