There's a really easy way to start the game out as Nod.... pick a flamethrower, wait for a harvester, throw your Timed C4 onto it before it goes into the tiberium field and flame the hell out of it. By the time your C4 goes off you should have whittled it down enough that it'll be almost dead, not to mention you get 200 points for killing it by yourself and a lot of cash. This can also be done with an engineer using both the timed c4 and the remote c4. No one ever expects this right off the bat, and if you time it right they won't be able to disarm the c4 because the harvester will be out in the middle of a tiberium field.
This is a lot easier than any of the aforementioned tactics because it doesn't require more than one person, although another can definitely speed things up. If you kill one harvester by yourself, you'll almost have enough cash for a Light Tank.