I eyeball the seasonings, but heres what you want:
About half the bottle of crab boil and 2-4 handfuls of Tonys. The Tonys has some kick so if you don't like it spicy then go easy until you get and idea of the flavor. Then you can add a cut and juiced lemon and lime, a quartered onion, a can of beer and cloves of garlic if you like. When it boils, add red potatoes and cut smoked sausage. When they are almost done, add corn. When the corn and taters are done add shrimp and cook 2 minutes. I like medium peel on shrimp. If you like it hotter, you can take it off the heat and let it soak. The longer you leave it the hotter it gets.
You can also do crawfish (live is better), crab legs, clams, mussels and scallops. I did crab legs and clams last time by pulling out the taters, sausage corn and shrimp and then steaming the crab and clams with the same water for about 5 minutes. Easiest way is just to look up how to cook each ingredient if you aren't sure.
Have fun, the low country boil has become a regular event around here.