I am still a rookie but I have gotten a lot of great advice from more experienced players. Below are what I believe are the three most essential ingredients of being a good rookie goalie.
1) Do not let slop in the goal.
This takes experience and practice and even the pros aren’t perfect at this. However, there are some things you can do to minimize slop. Fist of all you should pay attention to where the ball is at all times and position your men to minimize the chance of the ball going into your goal. No sleeping on the job. This is obvious when your opponent has the ball but it is also true when your forward has the ball. Be ready for the ball to come hurling at you at all times. Secondly, when the ball is approaching one of your back corner walls, you need to develop a habit of quickly positioning your goalie man so that the ball won’t slop into your goal behind your goalie man. Watch the good goalies when they play a match and when the ball is flopping around in one of their corners their goalie man instantly snaps into position to prevent the ball from sneaking in behind them.
2) Don’t let the ball enter your area and slip out.
If the foosball hits your back wall then it is your job to gain possession of it. If the foosball hits one of your men then try to absorb so it doesn't bounce back out. Being good at this will win you loads of foosball matches and make your forward happy. If you can’t gain possession of the ball then at least try and get a piece of it so the opposing three rod doesn’t get an easy grab. I good opposing forward will brutalize you if you don’t get good at this.
3) Find an extremely reliable way of clearing the ball from your area.
After you avoid letting slop in your goal and you gain possession of the ball you need to clear the ball from your area so your forward can do their job of winning the match for you. Giving the ball up to the opposing forward should feel like a slap in the face. Getting stuffed/roofed by the opposing forward should feel like a firm backhand.
If you can work to become very proficient at steps 1, 2, and 3 above then you should be on your way to winning lots of matches when you have a good foosball forward. Step 4 would be to improve your blocking skills. Step 5 would be to work on your shots from the back. However, I deemphasize those because they are not important when compared to stopping slop, gaining possession, and clearing the ball.
