I speak from hard earned experience and frequent mistakes !
The problem with scenary is that it can change all your best laid plans. Remember that plan you made where you lined up your forces on a notepad and assigned them their objectives ? (if you don't do this now, and you've been losing maybe you should try it). Well scenery can really put that proverbial spanner in the works.
Things to consider before deploying:-
1) Do your missile troops and artillery/war machines have line of sight ?
2) Can your support troops still be deployed close enough to the key elite units ?
3) Have you placed troops at the foot of hills from which your war machines will fire ?
4) Have you agreed line of sight with your enemy ? Note: some players allow hilltop units to be able to survey the whole battlefield with no restrictions.
To be continued...