Single best tip I can give you for grilling, is that you should line your grill with aluminum foil. And the reason is what cooks your food is infrared radiation, light that comes off your barbecue from coals. Sounds funny but that red glow, that's what's cooking your food. Actually a combination of the red glow you see and infrared radiation that you can't see but it's there and it's light and it reflects off things that are shiny.
So your grungy black barbecue, that means that the side of the barbecue is absorbing the heat not your food. So what you really want to do is line your barbecue with aluminum foil with the shiny side towards the coals. That reflects heat back up into the food, makes it cook faster and much more even.
The other great thing about barbecue is that a lot of flavor you get from barbecue is actually from fat dripping on the fire. So if you're cooking something that doesn't have any fat in it, like grilled vegetables, brush them with olive oil and brush them quite liberally because the olive oil that drips off and goes down and causes some flare ups, that will create a lot of flavor.