Remember, some of the tactics arent completely mine. I had to borrow other people's and learn from my defeats.
So heres my strategy. I assume most people use it, but idk. Mostly likely few. Here it is anyways:
One: secure your economy. You need cash to build a good military. Nuclear plants and powerplants for crystals and oil ships for oil fields. Dont squander your cash on barracks so early in game.
Two: build a land army. This is by far the most important unit in the game. Naval is restricted to water and air can be expensive and isnt effective at raiding bases alone. I generally view air as support. The regular infantry is the backbone of your military. I recommend doing a heavy spam, though its not exactly popular with some people. Build tanks AFTER you got a solid infantry army.
Three (1): assuming you are on a water map, build a navy. People have no idea how important a navy is. Besides transporting troops, combatting other naval units, and raiding enemy shipyards or oil rigs, this can blockade and cut off any support to your enemy especially on peninsula style maps like long islands. I recommend building destroyers if you are low on money (anti air, surface, and anti submarine), Battleships for bombarding and raiding enemy bases along with assissting blockade, and aircraft carriers (mobile airfield, upgraded transport, and a ton of hp plus damage). Transports generally are useless when you have aircraft carriers. Sell them as soon as you get one. I believe 1-2 aircraft carriers will be enough to transport your entire army. Blockade: position your ships individually around the peninsula. Make a line basically and space them apart (not too far, but not too close). Destroyers and air units can fend off air attacks or escapes and escape through air while your battleships and aircraft carriers can destroy sea units that attempt to enter or exit.
Three (2): if you are on a map that has no water, build a decent airforce before you start raiding. Heavy planes are recommended. Stealth bombers for raiding economy plants and infantry cant exactly attack it. (Except anti air ones).
Four: once you maxxed out on all units, then proceed to raid economy plants to cut off their money (assuming they got any left). Or you can keep your units at base to defend and invest on defense, though not recommend because its a big money drainer. Once you get money, you can invest on research and going nuclear. (Yea most experienced players will hate this). Keep in mind that only fire nukes can penetrate through shields.
Five (1): once you got the nuke ready, use it against their army (preferably land units) and once ready