You can one shot a GDI factory with a NOD nuclear strike if you aim it right, and you can usually win an attack against NOD bases in singleplayer by taking out the power plants first.
Ion Cannon can one shot Sam Sites and Obelisks of Light. Very usefull to know.
A very common multiplayer strategy is to build an APC carrying two Engineers and (usualy) three Miniguners. Make sure the Engineers get in first and last. You want to surprise them with an Engineer ASAP once you get there if that's possible, and if he dies then the Minigunners will cover fire for the second Engineer to hopefully capture something so you can build directly in his base (capturing a rafinery this early is often gameover).
When you capture Rafineries it's always better to time your attack so the ennemy Harvester is in the Rafinery. Capturing the building at that time let you capture the Harvester at the same time.
In multiplayer you can build Transport Helicopters and Commandos. If the ennemy is at the very top of the screen, you can try to "stealth" your way in with the Helicopter. Send it at the very top square at the other side of the map and then send the Helicopter on a square on the top of the map in the ennemy base. Only the shadow of the Helicopter will be visible and it won't appear on radar. Surprise!
There is a cheap bug in the unpatched version. When you sell units such as Rafineries or Silos, you get money for the amount of Tiberium left in the building but it still get transfered back to your other building. Build several Silos and then just keep building and selling them making sure they never get full. Endless cash supply without the use of cheat codes.
Try to micromanage your harvesters so they always leave at least one spot of tiberium at each patch they harvest. By the time they get to the tree or to the furthest patches, the nearest patches should have grown back enough for one full load.
Hotkey "x" scatter your squad randomly...
Miniguners owns Bazooka men.
Grenadiers owns Flamethrowers and weakly armored vehicles.
Flamethrowers own Miniguners.
Bazooka men can be devastating against flying units, weakly armored vehicles and small tanks. They owns Flame tanks if they are fast enough.
Group of Missile Trikes own undefended harvesters.
Groups of Miniguners own Obelisks of Light.
Mamooth tanks owns all.
That's mostly what I remember from the game. Been a very long time though.