Here's a tactic that I rarely see used. American LIs in V+ have the special ability to automatically entrench, even in enemy land. Entrench your LIs next to an important city and you can basically win the game, since you can't really beat entrenched LIs without massive losses, and Americans usually have a lot of LIs from TCA. Here's an example of me using it:
Entrenching is underused in general, and many players don't know how to entrench even with a general. The rule is that the unit has to be idle for 5 seconds before entrenching, and once entrenched, it must stay on stand ground, or it will move out of the entrenchment. So to accomplish entrenchment with the general:
1. Put your archers and LIs on hold fire (hotkey: shift+h)
2. Wait a couple seconds
3. Choose general and hit entrench (hotkey: b)
4. Put your archers and LIs on stand ground (hotkey: shift+g)
This can be really helpful when defending a chokepoint city on a map where the only attack can go through that city.
For Americans only, you can entrench LIs, even in enemy land, without a general, as I did above. This can basically win you a game if you entrench next to an important city:
1. Put your LIs on hold fire
2. Wait until the LIs entrench
3. Put your LIs on stand ground
While selecting troops, you can also use the scroll wheel to change the density of the formation, which can add to the firepower of the entrenchment. By default the formation is two deep, but with a lot of LIs a four deep formation may be a better idea.