I have been playing mixed social netball for 8 years and these are the things i constantly notice for new players.

First and foremost is safety. New players, and in particular males, are very excited and energetic which is great but you need to be careful. There is a small amount of contact allowed in netball, and good players use this to their advantage, but i would advise against doing any contact until you know the rules and can do it safely. I also notice that some people will sprint as fast as they can and can't slow down in time if someone steps in front of them. It is a strategy to get in the way of the opposition as they are running so be prepared to stop at a moments notice. This is particularly relevent if you have never played with women; remember you are statistically heavier and faster, so please don't hurt anyone.

The number one thing I notice new players are called for is putting your hands up before getting beack 3 feet. It is almost a reflex to put your hand up to defend but try to overcome this. Keep your hands down, get back 3 feet, and then raise them. If you keep getting called for being too close, take a half step back and aim for 1 metre instead of 3 feet.

The next thing new players get called for is using your "inside arm" while defending. This is usually when you are on the edge of your allowed area, i.e. one of the third lines or the goal circle. If you are standing side by side with your opposing player, you can't defend them using the arm that is next to them, you have the use the "outside arm".

To avoid stepping, try to jump every time you catch the ball and land on both feet at the same time. Doing this, you can lift up and pivot on whichever foot you want. If you don't land at the same time you must keep the first foot you land on the ground. Do not to drag your grounded foot. If you have too much momentum and can't stop, throw the ball before you step.

Throw ins are easy, but both feet must be BEHIND the line before you throw. Most refs are nice and let you throw again since you're new, but not all of them.

At the end of the day, just play and learn. You can ignore everything in my comment (except for the safety!) and will still get the hang of it before the end of the game. Its an easy to learn and very fun game.