So I am still a noob in playing FOG and learning a lot every week, so please be patient if this is all very well known to you
Deployment Area:
First of all buy an army (I will not discuss choosing units hear) and than use the Autodeploy function. In some cases, especially if you are playing a large army or if there is a stream or water on one of your flanks, this will enlarge your deployment area significantly. The size of the deployment area is calculated in relation to the autodeployed army.
Once you have your deployment area, setup your army. Keep an eye on terrain. In most cases it is not relevant in which terrain your units sits in, it is important where your unit will move to. Check if your units will get trouble with terrain in the next three or four turns. Be a scout and look were your army will move to. Some units like phalanxes or lancers need open terrain for some bonuses. Sometimes there is for example a track with trees, which is not open terrain, even if movement is normal. That can ruin your day. If you fight those units, try to bait them into some non open terrain.
So plan your units way and setup your units accordingly. Do check the height of all nearby hills. There is a significant difference of hills with height 100 or 200 but there are looking almost equal.
Forests are obvious, swamps and streams are not. So take your time to identify terrain and make it your friend
Seldom I advance with my army over the full width. In most cases I identify one flank to advance and deploy my units accordingly. In most cases this flank is overweighted and has a reserve of units. Once I see the troups of my opponent, I will double check my plan. Throw away your plan, if the deployment of your opponent will not allow it or if there is better opportunity. For example a cavalry attack on a flank with superior cavalry will fail in most cases, if enemy cavalry is supported by a lot of light units (bowmen or slingers). So drop your plan and think about something different. If you cannot win a flank be patient and buy time. There will be a a part of the battlefield with a superior position for you. Do not run into a battle you cannot win, just because it was your plan



