Your Fix
Start taking one-on-one or one-on-two lessons with a native teacher.
Be very clear with him/her that you would like to be corrected as soon as you make the mistake or as soon as you finish a sentence. Then ask for time to write down your mistake if you learn by writing.
If you learn best by listening and repetition, ask your teacher if it’s okay if you can record the lesson. Then you can listen to it while you’re in your car, jogging, or cooking.
If you’re on a Mac, you can easily do this by opening up the free program Quicktime Player and recording audio. If you’re on a PC, you can use a free program Sound Recorder and recording audio.
As you take care of your bigger mistakes, you can ask the teacher to focus on the small errors, too.
While this might sound expensive, it doesn’t have to be. Italki (which also offers free exchanges) and Google Helpouts offer affordable, customized lessons. It’s also possible that you can use Craigslist to find native teachers in your area if you like being in person. However, this does tend to be a little pricier.