1) Errors in parts of speech

There are 8 main parts of speech:
a) Noun - Noun basically means name.Name of person, place, animal, thing, feelings/ emotions etc. are nouns. Nouns are of the foll. types: Proper noun, common noun, abstract noun and collective noun.

Proper noun - Proper or particular name of person, place, animal, thing, feelings eg. Rajesh
Common noun - Class name eg. boy, girl, furniture
Abstract noun - Name of feelings and emotions eg. joy, friendship, anger
Collective noun - a set of or a group of things eg. an army of soldiers, here army is a collective noun and soldiers is a common noun
Some difficult collective nouns:
a brace of ducks, a murder of crows, a babble of barbers, a gaggle of geese, an eloquence of lawyers, a bench of judges, a parade of elephants, a number of mathematicians, a watch of nightingales, a pride of lions, a leap of leopards, a parliament of owls, a crash of rhinoceroses, a congress of baboons, a constellation of stars, an archipelago of islands, a quiver of arrows.

Nouns can also be classified as countable and uncountable:
For countable nouns (like students, benches...) one generally uses 'few', 'fewer','number'.
For uncountable nouns (rice, milk, sand,oil, diesel, petrol) one generally uses 'less', 'lesser', 'amount'

b) Pronouns - (Pro-for) Pronouns are used in place of nouns. eg. he,she,it,they,them,themselves,yourself,himself,her,his,our

c) Verb - Verb denotes action. Without verb one does not have a sentence.

d) Adverb - Adverbs modify verbs.eg. She sang marvellously.
Here marvellously is an adverb.

e) Adjective - Adjectives qualify nouns. eg. red apples. Red is an adjective.

f) Prepositions - These come before nouns/pronouns and denote relationship between words.eg. The cat jumped over the wall. Here 'over' is a preposition
Other examples include in, on, at, over, above, below, beneath, underneath, across, through, beside

g) Conjunctions - These join words, phrases, clauses and sentences (as well as other parts of speech) eg. and, either, or, neither, nor, if, so, hence, because, moreover, therefore, since
Contrasting conjunctions - but, yet, inspite, despite, though, although, even though
Conjunctive adverbs - however, nevertheless, nonetheless, whereas

h) Interjection - Words expressing deep feelings. eg, Wow, Hurray, Alas, Oh

Others include the foll. elements:
i) Infinitive - to + (verb). eg. to sing

j) Articles - a, an, the. 'a' and 'an' are indefinite articles and are used for only singular elements.'The' is a definite article and can be used for both singular and plural. Did you ever wonder why it is 'an honest', 'an hour', 'a united', 'a unique', 'a year', 'a unicorn', 'an MBA' ?

k) Participle - Verb which stops acting as a verb and begins to act as an adjective. eg. He is a confused man (He himself is confused)
eg. He is a confusing man (He confuses others)
Normally 'confuse' is a verb. In the above sentences, confuse is used as adjective. Participles can be past participle and present participle.

l) Gerund - Verb which stops acting as a verb and begins to act as a noun. Gerunds are also called as Verbal Nouns.
eg. My mother approves of my singing on stage.
eg. Swimming is my favourite hobby.
In the above sentences, 'singing' and 'swimming' are gerunds. Possessive (my,our) pronouns are generally used with gerunds whenever necessary.