How can you improve swimming speed?

Well, I'm still working on my backstroke myself, but a friend of mine gave me a REALLY good tip that's improved my speed by alot. When you reach the flags (that is, if there are any) start kicking your legs extremely fast. Once you're ready to, roll over onto your stomach and do your flip turn. Make sure you always try aiming closer to the floor after finishing your flip turn so you're gliding through the water. When you rise back up from the water, move your arms as FAST AS YOU CAN. This should help you when turning, but when you're actually swimming, roll your shoulders so they're moving in a circular motion. Also make sure you're reaching as far back as you can when using your arms. LAST THING. I don't do this, but apparently it helps. Try... bouncing in the water? I've tried doing it and it doesn't really help, but you could try it. Well, I hope I answered your question. If you already knew all of this though... then. Sorry.