> "sharpen" should be applied to the skill, not the person? ("sharpen your daily English")

Possibly depends on the dialect. "Sharpen your skills" is probably more common, but applying it to the person (e.g. "This will sharpen you up") sounds fine to me as a British English speaker (though if specifying a specific skill in the same sentence you probably wouldn't use that form).

> But I think the most glaring issue is the way you use commas (lots of unnecessary commas, comma splices, and parallel structure violations).

Definitely true, but that can also be a trait of some native speakers, FWIW. Some of my sentences have a ton of unneeded commas and "loose" clauses when I first write them, until I refactor them to make them more correct. It's certainly not exclusive to non-native speakers.

Yeah well, there's a lot to nitpick here... "language skills [...] varies" - a skill varies, but skills vary. Obviously I'm making tons of mistakes too, especially in a conversation (when there's no time to think and you can't go back to correct a phrase). Besides, being technically correct - in terms of grammar, vocabulary and so on - doesn't mean it sounds natural yet.

Thanks for your comments. I'll take note of these, and will revisit from time to time.

Most of the commas I use (before the "and" & "or"s) are Oxford Commas which dictates to use a comma before the conjunction if the sentences are separable. If the sentences are separable you don't use the comma. A more general rule is explained in [0].

My juries of my Master's and Ph.D. were very strict in this manner so I learned it the hard way. Now it's hardwired in my brain. Honestly I may be over using them, and will write more carefully.

[0] https://english.stackexchange.com/questions/30516/should-i-u...

> Most of the commas I use (before the "and" & "or"s) are Oxford Commas which dictates to use a comma before the conjunction if the sentences are separable

You seem to be confusing the Oxford (or serial) comma [0] used after the penultimate item of a list with the rule on comma + conjunction (or semicolon with no conjunction) separating independent clauses as opposed to a bare conjunction separating dependent clauses.

[0] https://en.m.wikipedia.org/wiki/Serial_comma

Generally the corrections were between independent clauses, and I made some research on the matter at that time. It's possible that I just mix the name of the rules since I got them from the back of my memory.

Thanks for clarifying these up. Will keep these in mind too.