Based on the considerable amount of writing corrected at The Linguist, the greatest problem that learners have is the inability to choose the right word, rather than grammar. Many people have a limited sense of the meaning of words. They are limited to a narrow dictionary definition. To fully understand how a word is used requires getting used to this word in many different contexts. Improving your use of words will become your main concern as you progress from the intermediate stage to the advanced stage. The Linguist system, with its emphasis on a wide variety of interesting content and the linking of words and phrases to content will help you achieve your goal of acquiring a rich usable vocabulary.
If you follow The Linguist program you will get used to the language, you will get much better at noticing words and phrases, your effectiveness in English will increase dramatically and your accuracy in choice of words will improve.
As a result your overall ability to express arguments logically and persuasively can come close to or even surpass that of native speakers. As mentioned earlier, even native speakers benefit greatly from The Linguist system.
You will need to take the last step and that is to learn to express ideas in a way that English readers will find logical and persuasive. You need to expose yourself to more and more interesting and enriching content. This might be professional content relevant to your business. It should also include audio-books from literature, philosophy, business writing, or other specialized subjects. You will want to study the way arguments are made and presentations organized in different settings and different cultures. You will also have a chance to practice this with The Linguist.
You can work on style, imitating some writers whom you admire by incorporating some of their favourite words and phrases via the linking method. You can also concentrate on issues like punctuation or complex sentences using The Linguist system.
You will find that using and improving in a new language is an ongoing adventure. You never reach perfection and you should not be concerned about perfection. Instead you will find that you are able to express yourself effectively in more and more situations that are important to you socially and professionally. Your enjoyment of the language will be enhanced by a sense of achievement as you are able to accomplish important tasks in English, without feeling that it was a great effort. At that point you will have reached your original goal. From then on you will continue to grow in the language, or you may think it is time to begin another adventure and start studying another language.