Many of the posts on this blog contain corrections of common errors in English.
But the best way to learn how to write and speak good English is to read and listen to good English.
Where can you find examples of clear writing?
Here is an extremely short list which is not meant to be exhaustive, nor does it guarantee that everything you read in these two publications will be perfect. However, I have found that the writing -- and editing -- in them is generally very good. You are welcome to suggest others in a comment on this post.
New Yorker -- Very well edited. Some superb writers selected to write for it. Notable for its unusual, but very sensible, use of the dieresis to show that a repeated vowel really is repeated, for example in "coōperate" instead of "co-operate" or "cooperate". This shows an active editorial policy. The people who produce this magazine are considerate towards their readers.
New York Review of Books -- Also very well edited and with a limited coterie of authors who write clearly and convincingly. For the past half century they have also benefited from a unique and highly-skilled cartoonist to provide portraits of authors and subjects.
Where can you find examples of good speaking?
You will have noticed that I frequently criticise the BBC for allowing the standard of English to deteriorate on both its domestic networks and on the World Service. There are, though, still some excellent presenters and artistes, especially on the more literate radio game shows, on the Beeb. For example, From Our Own Correspondent gives you the benefit of the BBC's widespread network of correspondents all over the world, talking at greater length than is possible in news broadcasts, often with telling personal anecdotes that help you to understand the background to the news.
In the United States (but of course accessible online worldwide) NPR (National Public Radio), in its various local guises, is excellent. In the morning you can hear Morning Edition, a programme (program) of news and comment which often contains some very good interviews, and in the afternoon and early evening there is All Things Considered. I also like the weekly Prairie Home Companion, a folksy mix of tall tales with radiophonic sound effects and music that the audience of thousands can sing along to, carried off with panache by Garrison Keillor, who also presents a five-minute programme each morning, The Writer's Almanac, which celebrates centenaries and birthdays of historical literary figures.
Try these out -- they are not very many, so it won't take long -- and let me know what you think.