Well, it's obvious, isn't it? You just plonk it down on your gaming board. Not so - here are a few things to think about when placing and using your terrain - board balance, placement, knowing your terrain, and special rules. Of course, the challenges posed by different types of terrain and landscape are part and parcel of the game. I am not suggesting that you eliminate this challenge, but there are certain pitfalls to be avoided.
Try to ensure that each side of the board is reasonably balanced in terms of cover, difficulty of ground and height of ground - unless you need a particular layout for a scenario or re-fight. This does not mean that the board has to be symmetrical or exactly the same on each side - it is more a matter of balance. One side could have more cover, but at the expense of it being surrounded by difficult areas of terrain. Another could have more high ground or buildings on one side but they could be difficult to capture or get into.
Be careful about the placement of terrain in deployment zones. Allowing deployment on a high building or hill with good lines of fire could seriously favour one side. Availability of cover in deployment zones is important too - especially for the person who goes second! Think about the placement of buildings and hills and don't disadvantage a player who has vehicles by making it impossible to get between them - life shouldn't always be easy but deliberately making things difficult for your opponent because you know they have large vehicles and you don't is a subtle form of cheating. Consider breaking up large areas of open ground with something that provides some cover - a few rocks or trees for example - otherwise it might become a redundant area because no-one wants to risk crossing it.
Having to stop and ponder about the effects of a terrain type in the middle of a game is frustrating and spoils the flow of the battle. Before commencing run through the terrain and agree that, for example, that river can't be waded, that slope or hill is difficult terrain, chain link fencing provides soft cover etc. Think about making up some terrain datafaxes that carry these details for easy reference. The datafax should include the armour value of the terrain, effect on movement, type of cover it provides, type or degree of obstacle, and any special rules that apply.
On the whole I don't recommend introducing lots of special or complex rules to do with terrain - it complicates the game too much. However, it can be interesting to use a special rule now and then. Why not leave some of the details about terrain to be discovered during the game?
When using rivers leave the decision about how deep they are, and therefore how easily they can be crossed, until someone reaches it during play. Place blank counters every 6 inches or so along one bank. When a trooper or vehicle reaches the river roll a D10, D20 or whatever. This becomes the depth of the river at that point. Write this on a counter and place it face down - your opponent must reach the river himself to discover the crossing points!
Chain-link and other fencing could have variable armour value or toughness rolled up when someone reached it. Once discovered this could be kept secret from your opponent. Why not try randomly deciding if the fence is electrified or protected by a stasis field or something.
These gameplays make scouts into true scouts, determining the lay of the land before the main drive begins.