To begin, initial placement of your cards can go a long way to helping you succeed. First off, you need to figure out the best way to allocate any terrain cards that you have received. While terrain always helps, it's important to remember that it will limit the number of cards that can be placed in a position. Thus, even if I have three or more terrain cards to use, I will generally keep one space clear, except in certain situations.
Woods are the best terrain for defense.
Hills are the best for offensive artillery at long range and defense in general. The creeks are good for limiting an attack and can come in handy if you are undermanned as the south often is. This is the situation when you are best advised to play all the terrain you can. Place a creek card on one of the flanks and protect it with one or two light units. The creek will limit an attack on your flank, and even if your opponent has a ford card to play, will limit the size of any attack to two cards, three if combined with a flank.