Offensive Strategies
Bridges are an important part of the game for Green. There are rivers close to your spawn, and if you get caught stuck in water, the blue snipers will not be friendly. Make bridges to cross the river quickly. Green's offense is at its best early on, when Blue has no defensive structures built to thwart invasion.
Once Green is in the Blue mountains, guerilla tactics can be used. A Green attacker can sneak up on or snipe at Blues and disappear into the ground again. The intel is also very vulnerable to Green tunnels; unlike Green's defense, which can remain passive as Blue is usually forced to make a frontal assault, Blue has to actively devote resources to thwarting invaders trying to tunnel under the intel. Even a small distraction can be enough to make a clean getaway. It's always better to evade the Blue fortifications, advance through the mountains and valleys, and carefully evade the hidden bunkers.
The Blue team is a frontal assault team and relies on a strong defense in the mountains to make progress elsewhere. In the early game Blue is at a major disadvantage, as the Green landscape is not favorable to simplistic sneak attacks. Blue's offensive constructions have to be systematic and well-planned; unlike Green's tunnels straight to the intel, Blue has to gradually make the landscape more favorable for themselves until they overwhelm any defense.
Blue's biggest advantage comes from building a strong defensive bunker in the mountains along the river; from this position, Blue can cover the river and parts beyond, preventing Greens from advancing, and allowing squads to make a beachhead on the other side. Green's bridges can be used against them as stealth tools when crossing the river.
Once across the river, Blue can sneak along the coast, but they should also build small amounts of cover to aid further progress inland. Tunneling is difficult, since many areas of the Green landscape only allow you to build a trench one block deep, but if care is taken to camouflage the entire tunnel as it is built, major progress can be made over the course of a game.
 Defensive Strategies
Green uses bridges to ease travel across the rivers. However, Green has to be careful about overbuilding; unlike Blue's sprawling mountains, their defensive strength lies in the landscape being very flat and hard to sneak around in. If towers and bridges become too elaborate, Blue can start to use them against Green. Instead, Green defense should focus on simple structures with high visibility, while thwarting Blue's attempts to build. A successful Green defense will allow the Greens to cross the river and take over the mountainside.
Blue's best defense is to take control of the mountains as quickly as possible. Once the Green are inside they can run amok and dig their way to the intel. In doing this, they have to thwart Green's plans to build bridges and cross the river. The best way to do this is to gradually grow sniping positions that favor the Blue side, using one-way tunnels and elaborate trench systems. Once snipers are in place they can destroy bridges and eliminate attackers crossing the river. It's faster to build a wall or a trench than a tower, so bear that in mind if you're on a busy map. Try to create chokepoints in valleys or rivers, for it is much better to form a defensive area than chasing after the opposition tunnellers.
When guarding the intel, Blue has to patrol actively for potential diggers; the mountains reduce visibility too much for Blue to be able to rely on a good construction alone.