One of the first things to remember is to practice regularly. That means you really cannot achieve higher level if you practice once or twice a week. So you should practice every day even if it means only 30 minutes a day. If on some days you only have 15 minutes available, repeat previously mastered material. That counts.
Also in each practice session you have to have a clearly defined goal. This means that whenever you sit down on the organ bench you should have a clear vision of what you are about to accomplish in this practice session. This goal can be very small, for example, learning these difficult four measures of your piece, memorizing a section of music or repeating previously mastered musical material.
Your organ practice also has to be wise and you should aim to correct your own mistakes. Too often I see organists make mistakes while playing organ and they don't stop and don't correct them. They would just keep going until the piece is over. This is an incorrect approach to practice.
What happens is that if you don't correct the mistakes, they just keep coming back the next time you will be playing this piece. Therefore, you have to correct your mistakes right away. But you should not stop here. You should aim for at least 3 correct repetitions in a row.
There is one more thing which helps to improve sloppy organ practice habits which is practice in fragments, separate voices and voice combinations in a very slow tempo. If you practice in this manner, you can control your movements and playing much better. Therefore, if you make any mistakes, you will easily correct them right away.
Try to apply my tips in your organ practice. Keep in mind your goals, practice regularly and be persistent in correcting your mistakes. This will help you advance in organ playing and achieve the results that you want.