We thought we'll share some of our thoughts on the most common errors made in these forums so that a significant number of errors of language are eliminated. We guarantee that everyone who just follows these religiously will avoid 80% of language errors.
We'll divide this into 2 sections: punctuation and grammar.
PUNCTUATION (in descending order of most frequent errors)
Punctuation is the use of commas, colons, hyphens etc.
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Correct: "I did talk to him - in fact, thrice."
These are two different parts of a sentence joined by a hyphen. In these cases, there are spaces both before and after the hyphen. You should not write
Wrong: "I did talk to him-in fact, thrice."
or
Wrong: "I did talk to him- in fact, thrice."
Both are wrong.
Correct: "He looked worried (which worried me too), but seemed in no mood to give up."
After the closing bracket above, there is no space, which is against the rule that after every punctuation mark there is a space. This is the third case. This is because there is never a space before a comma or full-stop - our next big rule.
: (colon)
; (semi-colon)
! (exclamation)
That is, no space before, and always a space after.
"it's" (with the apostrophe) is just short for "it is". That's it.
"its" (without the apostrophe) means belonging to "it", the possessive case. ("Its legs were weird").
"let's" (with the apostrophe) is just short for "let us". That's it, again.
"lets" (without the apostrophe) is used, simply put, in cases which are not "let us" - like, "He always lets us in."
They should be "doesn't" and "aren't". The single quote stands for something missing in the short form, which in these cases is an "o". Similarly, 'n' for "and" (as in Guns 'n' Roses), 'cos for "becos" (which itself is an illegal spelling, actually, but you really don't care) etc.
Example:
Wrong: "The song Pardesi pardesi jana nahi in Raja hindustani is quite good…"
Correct: "The song Pardesi Pardesi Jana Nahi in Raja Hindustani is quite good…"
Pardesi Pardesi Jana Nahi is the name of a song and Raja Hindustani is the name of a film, so all words start with capital letters.
GRAMMAR
Again, very involved, but we present here some common errors, in the decreasing order of frequency.
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The most common grammatical flaw. If you get this right, you are good. Look at this sentence:
Wrong: "Divine Comedy, the great Italian classic was written by Dante."
Correct: "Divine Comedy, the great Italian classic, was written by Dante."
The phrase "the great Italian classic" is called a relative clause. It is characterized by two things:
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Most people do not put the second comma several times. Remember, if the part can be removed with the sentence still being grammatically right, then it either has commas both before and after, or (in some cases) neither before nor after. But not just one comma.
Other examples of relative clauses:
Correct: "Even summer, normally a season characterized by high temperatures, is pleasant in Australia."
For practice, pick up any daily newspaper (except perhaps The Hindu's main edition), and try to find such errors. They abound

If you want to insert a sentence/phrase in another sentence, do it using hyphens:
Correct: "I never wanted to see him again - and I don't suppose he wanted to see me either - but fate decreed otherwise."
Here again, the part between the hyphens can be removed with the sentence still being grammatically correct.
Look at this sentence:
Wrong: "None of us are capable of that."
None is short for no one, and so is singular. In effect, this sentence reads, "No one of us are capable of that." Obviously, it's wrong. It should be, "No one of us is capable of that." Or, as
Correct: "None of us is capable of that."
Here the subject of the sentence (none) was singular, and its usage (are) is plural, which is wrong. This one (stuff starting with none) is a popular error.
Other examples of such mistakes:
Wrong: "Everyone of the members, including life members, were asked to show their tickets."
Correct: "Everyone of the members, including life members, was asked to show his/her ticket."
Wrong: "She is so fastidious that neither of the three houses were liked by her."
Correct: "She is so fastidious that neither of the three houses was liked by her."
(Neither here stands for not even one.)
Wrong: "He is one of the shrewdest men that is in the organization."
Correct: "He is one of the shrewdest men that are in the organization."
(There are multiple shrewd men in the organization, and he is one of them.)
Wrong: "Neither of the two students suspected in the 'missing-girl' case have so far been arrested."
Correct: "Neither of the two students suspected in the 'missing-girl' case has so far been arrested."
Wrong: "The lioness with her 4 cubs were caught by villagers and sent to the zoo."
Correct: "The lioness with her 4 cubs was caught by villagers and sent to the zoo."
Look at this sentence:
"I know few people who can do it."
This sentence does not mean that I know some people who can do it. It means that there are very less number of people - or actually no persons - who can do it. If you want to say that you know some people who can do it, you should say:
"I know a few people who can do it."
Which of these is correct?
"I have oranges, peaches and pineapples."
"I have oranges, peaches, and pineapples."
We at fullhyd.com believe the first, where there is no comma before "and". Now look at this - which of the following is correct:
"I have known him since childhood and his principles have always been beyond reproach."
"I have known him since childhood, and his principles have always been beyond reproach."
Here, the second, where there is a comma before "and", is correct.
The logic is that when you are giving a series of similar things (fruits in the first case), then the and before the last object is not preceded by a comma. But if you are joining two different phrases with an "and" as in the second case, then there is a comma.
Psychologically, when you put a comma, it means you want to stress the part following it - if you were speaking that sentence out instead of writing it, you would perhaps take a small pause there. Rather subtle, but you'll get the hang as you write (and read and speak) more and more English.
More examples:
Correct: "He's dead and gone to heaven."
Wrong: "He's dead, and gone to heaven."
Now "dead" and "gone to heaven" are not exactly similar things like fruits, but both of them use the "He's" as their beginning - that is, instead of writing "He's dead and he's gone to heaven", we are writing "He's dead and gone to heaven", and so "dead" and "gone to heaven" are similar in this context - they both join "He's". Hence no comma before "and".
Similarly,
Correct: "I met him, spoke to him and convinced him."
However, in both the above cases, you can still put a comma before the "and" if you think the last part needs to be stressed (as we noted earlier).
Correct: "Many of them failed the test, and some of them failed to score any marks at all."
These are just common errors, but taking care of these will make your writing at least 80% accurate. Like we said, we just wanted to point out common stuff.