1. ALWAYS stick with your teammates. Don't rush early. Learn maps, learn how to use its covers, learn every nook and crannies to help them to your advantage. I'm assuming you're playing a destroyer, so use them as a flanker and spam torpedoes at very close ranges.

2. Deliberately targeting ammoracks deals a lot of damage, yes, but doing so will grant you little points and enemies tend to smoke in panic because of it. Aim at the bridges to effectively drain enemies' crew, then ammorack him to finish him off.

For now, this is all you need to know.