I like to work in f/stops (even in the darkroom). I make my test strips two stops down from wide open on the lens (the sharpest aperture) and use the following sequence: (This is done by covering a small part of the strip with each new exposure, not uncovering)
1 second, 1, 2, 4, 8
If you make a 1 second exposure, then cover a little, another second, cover more and so on you end up with an exposure series that provides 5 full stops of exposure. If you add up the exposures you get 1 second, 2, 4, 8 and 16. Other than the fact that making the exposures in a sequence creates a small inacuracy in the times (because adding the exposures is not exatly the same as making one 16 second exposure) you get a five stop range.
If you are still underexposed open up all the way and try again. If you are too dark, close down and make another test.
Another suggestion is to test strip different parts of the image. Sometimes the foreground and sky in a landscape (for example) need radically different exposures. Instead of trying to guess about dodging or burning, test them individually and get accurate exposure times. This makes printing a lot faster.