get a tripod, make share it doesn't shake.
shoot straight not at an angle.
macro lens is not needed unless you want to shoot really close up pics.
any low f stop lens will do. I've shot with a 50mm 1.8 before, and it turns out nice.
Don't need very expensive equipment to shoot decent pics, I've got nice pics from iphone.
don't really need to shoot raw, jpeg is fine for most beginners. if you shoot a nice pic, little to no post editing is required, maybe just a few adjustments (very minimal) in photoshop should be fine. shooting raw and doing lots of post edit for newbs is too complicated, it's a whole another game on it's own....
for coral pics and really close up pics, you wanna try to shoot manual focus because it'll focus exactly where you want (1/2" off the coral and focus is wayyyyy off). for fish pics, you're gonna want to shoot autofocus with a pretty fast lens.
as for color, you have to pretty much do a manual white balance setting prior to get the color you want.
MOST IMPORTANT TIP: practice, practice, practice.......
here's a few for you (in my other lifetime, i was a photographer):

