Envy and Jealousy

  The word “envy” implies a longing for someone else’s good fortunes. 
 “Jealousy” is far more nefarious. It’s a fear of rivalry, often present in sexual situations.
 “Envy” is when you covet your friend’s good looks.  
 “Jealousy” is what happens when your significant other swoons over your good-looking friend

Continual and Continuous

They’re similar, but there’s a difference. “Continual” means something that's always occurring, with obvious lapses in time. “Continuous” means something continues without any stops or gaps in between.
   e.g., 
           The continual music next door made it the worst night of studying ever. 
           Her continuous talking prevented him from concentrating.

Lay and Lie

This is the crown jewel of all grammatical errors.
               “Lay” is a transitive verb. It requires a direct subject and one or more objects. Its present tense is “lay” (e.g., I lay the pencil on the table) and its past tense is “laid” (e.g., Yesterday I laid the pencil on the table). 
                “Lie” is an intransitive verb. It needs no object. Its present tense is “lie” (e.g., The Andes mountains lie between Chile and Argentina) and its past tense is “lay” (e.g., The man lay waiting for an ambulance). 
       The most common mistake occurs when the writer uses the past tense of the transitive “lay” (e.g., I laid on the bed) when he/she actually means the intransitive past tense of “lie" (e.g., I lay on the bed).

Which and That

This is one of the most common mistakes out there, and understandably so.
     “That” is a restrictive pronoun. It’s vital to the noun to which it’s referring. e.g., I don’t trust fruits and vegetables that aren’t organic. Here, I’m referring to all non-organic fruits or vegetables. In other words, I only trust fruits and vegetables that are organic. 
      “Which” introduces a relative clause. It allows qualifiers that may not be essential. e.g., I recommend you eat only organic fruits and vegetables, which are available in area grocery stores. In this case, you don’t have to go to a specific grocery store to obtain organic fruits and vegetables. 
        “Which” qualifies, “that” restricts. “Which” is more ambiguous however, and by virtue of its meaning is flexible enough to be used in many restrictive clauses. e.g., The house, which is burning, is mine. e.g., The house that is burning is mine.

Who and Whom

This one opens a big can of worms. 
      “Who” is a subjective — or nominative — pronoun, along with "he," "she," "it," "we," and "they." It’s used when the pronoun acts as the subject of a clause.
      “Whom” is an objective pronoun, along with "him," "her," "it", "us," and "them." It’s used when the pronoun acts as the object of a clause. 
       Using “who” or “whom” depends on whether you’re referring to the subject or object of a sentence. When in doubt, substitute “who” with the subjective pronouns “he” or “she,” e.g., Who loves you? cf., He loves me. Similarly, you can also substitute “whom” with the objective pronouns “him” or “her.” e.g., I consulted an attorney whom I met in New York. cf., I consulted him.

How to use A LITTLE, A FEW, LITLLE and FEW

a little/a few and little/few:

A) a little/little (adjectives) are used before uncountablenouns:

a little salt/little salt a few/few (adjectives) areused before plural nouns.

a few people/few people All four forms can also be used aspronouns, either alone or with of:

Sugar? ~ A little, please

Only a few of these are any good

B) a little, a few (adjectives and pronouns)

a little is a small amount, or what the speaker considers asmall

amount, a few is a small number, or what the speaker considers asmall number.

only placed before a little/a few emphasizes that thenumber or amount really is small in the speaker's opinion:

Only a few of our customers have accounts But quite placedbefore a few increases the number considerably:

/ have quite a few books on art (quite a lot of books)

C) little and few (adjectives and pronouns)

little and few denote scarcity or lack and have almost theforce of a negative:

There was little time for consultation.

Little is known about the side-effects of this drug.

Few towns have such splendid trees.

This use of little and few is mainly confined towritten English (probably because in conversation little andfew might easily be mistaken for a little/a few). Inconversation, therefore, little and few are normallyreplaced by hardly any A negative verb + much/many isalso possible:

We saw little = We saw hardly anything/We didn't see much.

Tourists come here but few stay overnight =

Tourists come here but hardly any stay overnight. But littleand few can be used more freely when they are qualified byso, very, too, extremely, comparatively, relatively etc. fewer(comparative) can also be used more freely.

I'm unwilling to try a drug I know so little about

They have too many technicians, we have too few

There are fewer butterflies every year.

D) a little/little (adverbs)

1 a little can be used-

(a) with verbs: It rained a little during the night.

They grumbled a little about having to wait.

(b) with 'unfavourable' adjectives and adverbs: a little anxious a little unwillingly

a little annoyed a little impatiently

(c) with comparative adjectives or adverbs:

The paper should be a little thicker

Can't you walk a little faster?

rather could replace a little in (b) and can also beused before comparatives (see 42), though a little is moreusual. In colloquial English a bit could be used instead of alittle in all the above examples.

2 little is used chiefly with better or morein fairly formal style'

His second suggestion was little (= not much) better thanhis first.

He was little (= not much) more than a child when hisfather died It can also, in formal English, be placed beforecertain verbs, for example expect, know, suspect, think:

He little expected to find himself in prison He little thoughtthat one day Note also the adjectives little-known andlittle-used: a little-known painter a little-used footpath

GRAMMAR:
While speaking English or any languages,some rules are followed.That rules can be said as Grammar.