Jedidade, that's exactly how we do it... streaking paint drops. Also, using thinned down rubber cement and applying it lightly in a couple of thin layers, then painting that. The bonus there is that you can take the cement off after you've finished shooting, and return the model to a more pristine condition.
As for airbrushing streaks, get some silly putty or a bit of that blu-tac poster hanging stuff... press it on so that you get a bit of a lip where you want the front of your streak. This is a soft-edge mask, and you want to use this to 'harden' the front edge of your streak, to give the bolt, beam, whatever an actual impact point.
Never, ever, ever use black until you kow how to tint and use warm and cool darks. Black is what you get from carbon flashing, but is really only best used on about :16 to :12 scale or higher.
Remember, if you have a :24 (for example) scale model... holding it 1 foot away from you, it should look as if you are standing 24 feet away from the real deal, etc... even at 20 feet or so, you get all kinds of interference in the colors and unless you are in a very overcast environment and focusing directly, a lot of values will be lost to you. Squint tests for value will help you see if you've gone dark enough.
edited this for a couple of dippy spelling errors