It is a trite observation to make that it is not enough if one’s use of a language is grammatical; it should also be idiomatic.  It is on this latter count that the English of quite a few well-educated non-native speakers   has to be faulted.  I only spotted the error in the calculation may be clear enough. But it is both ungrammatical and unidiomatic.  Ungrammatical because only is not used in this way in English; unidiomatic because the proper way to bring out the meaning here is with an introductory it. It was I who spotted the error in the calculation.  A sentence was …is a favourite construction with The Hindu.  But the required structure here is: There was a sentence….
These remarks are by way of a preamble to what I am now going to quote from the latest monthly release by the founder of a much-advertised B-school. The article is about Mayawati’s resounding victory in the recent UP elections and its significance.  ‘She should better remember that the voter’s loyalty cannot be taken for granted for ever’—‘India: Today & Tomorrow’. May 29, 2007.
‘She should better remember’. The idea is idiomatically expressed by using had.  She had better remember. This is usually contracted to She’d better remember.
‘Somebody had remember’ is used to give advice about what someone should do. You‘d better stick to your present job. / Your mole seems to be growing.  You’d better see a doctor. /  You’d better sell your shares before the market goes down further.
Advice can turn into threat. You’d better keep your mouth shut.
The writer could have said: ‘She should remember that the voter’s loyalty cannot be taken for granted….’ But this lacks the warning implied in had better.
The better discussed above is different from the comparative better (good. better, best) as can be seen from a sentence like You’d better do better next time.  The second better is the comparative. The first one is the better used idiomatically to suggest an implied warning. Some common phrases with the comparative better are: It would be better to go over the calculation again.  (With the idiomatic better we would have You’d better go over the calculation again.); better luck next time; You would be better off (or you’d be better off) without his advice; There’s nothing better than a hot cup of coffee on a cold morning; Better late than never.
This better has an idiomatic use in to get the better of someone, meaning
‘to defeat, outwit or outsmart someone ‘. In the recent UP elections Mayawati got the better of Mulayam. To go one better has a similar meaning but it suggests that you defeated your opponent by playing his own game. The DMK offered each hut- dweller 2 kg of rice.  The AIDMK went one better by offering a stove, 5 liters of kerosene and a vessel to cook the rice.
Some famous phrases with the comparative better are: the better half  (this could be the husband or the wife but is usually intended to refer to the wife. A disillusioned married man was heard to refer to his bitter half.) And then in most (or all) religions the man woman are joined in holy wedlock ‘for better or worse, until death do us part.’ The phrases are still current, even in today’s society where every thing is disposable, from a needle to a partner.
Another phrase which is in fact an idiom but is often used literally and incorrectly is: the done thing. Here is a citation: The tests are a done thing and there cannot be any going back them –DH 14 May, 1998, p.8.
What the writer means to say is that the tests have been gone through (done)—whether somebody likes them or not. (The reference is to atomic tests by India.) No point in talking about them now.
But the done thing means: ’what is socially acceptable.’  It just isn’t the done thing to call teachers by their first names—Longman Dictionary of Contemporary English. (In England perhaps but not in the US. In India generally it is ‘Sir’; in Karnataka: ’Sa, Sa…’) It is not the done thing, in the west, to burp at the dinner table.
Many things can go wrong in the use of idioms. I have examined two kinds of slip: not using the correct idiom to express a certain idea (should better instead of had better); using a set of words which constitute an idiom in a literal sense (the done thing). I am sure the attentive reader will find more examples of these incorrect usages.
(The remarks about the done thing should not be taken to mean that an idiom can’t be used literally. It takes some ingenuity to do so.  Here is an example: Never more at home than when at home—Kay S. Wye.)
Maxims and Observations of Kay S Wye
In the transition from absolute monarchy or colonial rule to a true democracy, there may be rule by War Lords (as in certain African countries) or venal politicians (as in India).  
(The author can be contacted at ksyadurajan@yahoo.com)