For a thin steak like a flank or spalla, the fire should be very hot, and the cooking times can be as brief as two or three minutes per turn. At that pace, you'll probably need only two turns per side. Sear one side and then the other. On the second pass, cook the steak at a 90-degree angle to its first position to get those attractive seared grid marks. Don't cook beyond the rare side of medium-rare or it'll be dry and tough.
The two-stage fire
For steaks such as tri-tip that are more than three-quarters to an inch thick, remember the value of a two-stage fire. Once the coals are lighted, arrange them against one side of the barbecue so you have one area of the grill that's very hot and another that's more medium. (If you're cooking with gas, turn one side to high and the other to low, or turn it off entirely.)
Sear the meat on both sides over the hot fire, then pull it over to the cooler side, turning it from time to time. You can push these to the medium side of medium-rare.
No matter the thickness of the steak, don't forget to let it rest after you've removed it from the grill. This lets the meat finish cooking and the juices settle.
It might seem that it can't make that much of a difference when a flank is only a half-inch or so thick, but it does. Carved right off the fire, the center appears spongy and juice flows everywhere. Given five minutes' rest, the meat is cooked more evenly and there's much less moisture loss.
When serving the leaner steaks, also remember that sauce covers a multitude of sins (both literally and figuratively). You can gain a bit more margin of error doneness-wise by spooning it over the meat. Even if it's something as simple as good olive oil with a tease of lemon, that little bit of extra fat can be enough to rescue a flank steak that somehow went from the rare side of medium-rare to the medium side while you were finishing that last beer.
If you want to get a little fancier, what about a smear of tapenade, or a spoonful of aioli? One of my favorite steak sauces is an Argentine chimichurri, basically a kind of pesto made mostly from parsley with a to-taste assortment of other herbs tossed in. (I like a bit of mint and some dried oregano; other possibilities include dried chile, cumin and fresh oregano.)
A true chimichurri is made by whisking a quickly made brine (salmuera) into the herb mixture and letting it steep overnight. But a fast version can be made by leaving out the brine. It doesn't seem to improve over time the way the original does, but it's still plenty good as a last-minute finish for a steak. Brush a couple of tablespoons onto the meat before grilling as well.
Carve the meat in thin slices, cutting across the grain and holding the knife at a pretty shallow angle so you're slicing on a deep bias. The steak will fall away in wide, thin ribbons, seared on the surface and reddish pink at the center. Spoon a little sauce down the center and pass the rest at the table.
The flavor is deep and beefy with a wild herbal overtone. And unless you tell someone how much you paid for it, they'll never guess.
Congratulations, you've just won the cheap steaks sweepstakes.