Pretty much covered in the thread, so let me just list it:
-could be a bad atmosphere - stuff between you and the moon can affect IQ a lot, as can ambient light. Only thing you can do is drive away from a city, someplace with clean air.
-filters: a bad filter can really affect sharpness and contrast
-shutter: way too long, at 4 seconds the moon is zooming past you. Try a fraction of a second for the moon. For the moon you can go to 1/180 if the tripod is sturdy and you probably won't need an exposure longer than that
-Aperture: The moon is lit by the sun, so its actually pretty bright. Use the aperture that your lens is best at. Usually this is between f5 and f11, but it depends on the lens. You are focusing at infinity anyway, so DoF probably won't matter. For your lens f8 is probably the sweet spot.
-ISO: 100 or 200, but don't be afraid to go higher if needed. For the moon, you probably won't need to go higher, though.
-Use a tripod and 2 second timer (the remote was a good idea, use that)
-Use Manual settings (f8, iso100, 1/180) or spot metering in Av mode.
-If you have filters, you probably won't need them. If you have a lens hood, put it on, it can't hurt.
-300mm is good, but we are used to seeing wonderful closeups like the one Wildman posted, so it might seem underwhelming by comparison. Don't let that discourage you. You can only get that good by doing it
The reason we can give you detailed tips is because the moon is pretty constantly lit by the sun, pretty much where ever you are.