Now that I have worked with over 6,000 clients across the globe in helping them with their careers the overriding reasons why clients come to me for help are:
Communication, and
Relationships
in that order. What do I mean by this? Most clients do not realize that just doing great work in their role is merely table stakes. Many, especially immigrants, believe that their work speaks for itself. They fail to realize that what makes that work more valuable to them, to the workgroup, and to their company is how they manage communicating what they do in their role using the right medium and how they manage their relationships with others in their workgroup and up and down the chain of command. Even for good relationships strong communication skills are the sine qua non on which such relationship can be built, nurtured, and expanded.
Working with clients throughout my coaching career I have come across many situations where my clients were truly outstanding in their work performance, but because of their inability—and sometimes indifference—to communicate what they do (or did) and their inability to manage relationships with their peers, superiors, and others they often did disservice to how that work translated in their career progression. In existential terms it translates into lower salaries, passing over for promotions (read my blog of Oct. 15), and lowering your stature in the organization where trumpery reigns. In many cases the good work my clients did got sidetracked or hijacked by someone else, who then takes credit for it because of their superior communication, political, and relationship-management skills.
I am not suggesting that you build your communication and relationship-building skills to do such things for yourself to advance your career, but I am suggesting that without strong communication and good relationship-management skills others will always sidetrack your stellar work because they surpass you in such key skills, which are often valued more that stellar work performance, despite their own mediocre work performance.
One of the most dramatic examples of how lack of good communication (and presentation) skills can defeat you in an important meeting is evidenced by someone when they take your original idea that you presented in that meeting, but where it failed to get any traction during the course of your air-time because of your lack of strong communication and presentation skills (confidence and conviction). Then someone with good insight and strong communication skills hijacks that idea, re-articulates it in a much more impressive “package” a little later in that very meeting, and everyone rallies around that idea, even attaching their own name to the idea you originally proposed. You walk away feeling defeated, shaking your head, when the executive chairing the meeting asks you to help that person operationalize “their” idea.
So, what are some of the ways you can master strong communication skills and overcome these typical obstacles to your career growth? Here is my list:

I Words and their usage
These resources send you a daily email with a new word, its usage, and etymology, etc.
1. Merriam-Webster Dictionaries: www.merriam-webster.com will email you a word every day for free. It also offers a paid on-line dictionary for an annual fee.
2. Wordsmith is run by Anu Garg and is also a free email service that sends new words every day. This is a great resource for a variety of reasons. www.wordsmith.org
3. Oxford University Press: Oxford Dictionaries Online provides free email service with daily words and their usage. Contact wordoftheday.odo_us@OUP.COM It also offers subscription services
4. There are many online dictionaries available for free. Just Google your interest, (e.g., Dictionary of Urban Slang) and find what you are looking for.

II English Writing
1. The best resource for improving your writing skills is provided by the Purdue University through its Online Writing Lab (OWL). https://owl.english.purdue.edu/owl/ This rich resource offers a variety of avenues for you to improve your verbal skills through online exercises that allow you to visit different areas of your need: Grammar, Composition, Word usage, Pitfalls, etc.
2. Other resources can be found through Google and other searches.
3. If you want to improve your written English make a habit of writing something every day.
4. Writing That Works, 3E: How to Communicate Effectively in Business (Roman & Raphaelson)

III Speech
1. Several YouTube resources are available to improve your speaking abilities in both the US and British English. Rachel’s English is a channel that has many exercises and content (US)
2. Anglolink (By Minu) this is a UK-based version of English
3. There are many other providers of this content on YouTube.
4. There are also many excellent TED talks on communication, presentations, and body language. Watch them again and again and practice some of the tips offered in those talks.

IV Public Speaking/Leadership Communication
The best resource for improve your public speaking skills is the Toastmasters International. There are local chapters in every city, organization, and company. So, find a local chapter and sign-up. https://www.toastmasters.org/ Although not entirely free it is almost free.

Please check out these and other resources to improve your communication. Make it a habit to learn how to make your communication and presentation better every day. It is well worth the time and energy you spend doing it.
Good luck!