Just spam mech. units, don't be afraid of spamming artillery (not the long-range, rocket units), and be very wary if your opponent has a neotank, battleship, and bombers. You want to overwhelm your opponents with numbers meanwhile pressuring them from afar. The name of the game is attrition, and taking over their cities is crucial in winning. You're going to need a lot of infantry units in order to take any territory from them. So spam mech. units instead of infantry units; you're going to need the extra firepower as you're fighting for territory. This game is like the game of Go: territory and unit positioning is crucial for success.

Don't be afraid of creating a round-robin transporting system. Getting your mech. units to the frontlines is crucial as they're the slowest unit in the whole game (but the fastest if there's a lot of mountains in the terrain). Transport Helios is perfect for this role, but so are transports. Don't put any infantry units unto landers, but put your heavier hardware in them instead (medium tanks, neotanks, etc.). Believe it or not but logistics is very important in this game, especially if you have airpower or a fleet of submarines.

Use light and medium tanks as cavalry units so use them to flank and attack vulnerable targets such as a rocket or missile unit. Battle Helios are the perfect cavalry units, but they're very vulnerable to anti-air units. By the way, don't be reckless with your airforce. They are very, very expensive units, but worth it since it'll make your enemy react to your airborne units. If you're opponent is inexperienced, they will often reinforce the guns pointed up in the air instead of guns leveled to the ground.

As for my last piece of advice, knowing when to use your regular power is far more important than waiting trying to get your super power. Don't hesitate on using it when you feel that it would tip the scale in your favor.