I suck at crucible. Never played too much but I've improved from about 0.5 or less! to 1~1.5 and only play for my daily marks now. My advise, as someone who suck but improved a little, would be to learn the maps slowly, and don't play aggressively until you know them. Following your teammates could help to learn that. Try a few famous different weapons until you find something you like and that fits your current style. Ex, if you're taking your distance while get used to the maps, an scout rifle would be the best choice and a secondary short range weapon like a shotgun or a side arm. And last, be aware of the heavy weapon synths spawn spot and time. You can take them and have some free kills, or ambush people who want to take it. But if you're nowhere near it, you'll be in a huge disadvantage.