Build a "wall" around Tiberium when playing against the CPU. Make sure to also close up the entrances to your base. Then, press R to display the surrender option. Do not press anything else and wait for some length of time. Then, choose the "Cancel" option. The Tiberium amount should have increased on the map. Note: make sure the Tiberium is "regenerateable".
Controlling air units
This trick works for both the GDI and NOD. To control air units in midair, simply give the helicopter a team number. This allows you to give multi strikes without reloading.
Destroying the Temple of NOD
Surprisingly, the CPU NOD usually keeps its Temple in a small second base, apart from its main base. This base is also usually very poorly defended. There will usually be only one Obelisk guarding it, however they also usually fill it with SAM sites making an air attack futile. Also, the CPU will not use the Nuclear Missile until the Temple is attacked, and for good reason -- there is only one nuke attack allowed per game per player. First, build a second base large enough that you can still fight if your first one, or it, is destroyed. Then, get a large army and mass it outside the base close, but far enough away to be out of range of the enemy's Obelisk. Get an Ion Cannon shot ready and use it to attack the Temple. It will fire its nuke at one of your bases, destroying it. However, now they have used up their only nuke and you do not have to worry about it anymore. Order your army to swarm the base, first taking out Obelisk, then any Turrets, then everything else except for one building. Take over the building, barricade the base with walls, then build walls or buildings over where they had buildings so they cannot rebuild them.
If you want to protect a certain units (for example, an ore truck) select a vehicle then hold [Ctrl] + [Alt] then click on the unit you wish to protect. It will follow it around for protection.