You can train your grammar skills here.
1.Go to the websites Tolearnenglish, English Grammar Online, Polseguera, Testy, BBC Grammar Challenge, Guide to Grammar, Agendaweb, First English.
2.Choose Beginners/Intermediate/Advanced level (Level 1, Level 2, Level 3, Level 4).
3.Choose any exercise you'd like to take. Solve it.
4.Post the name of the exercise, the link and the mark in the thread. You can post difficult/favorite sentences there.
5.Don't try to cheat us by posting fake marks, we know your real progress : )
6.Take quizes on our website
Articles

You should try the next tests.
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BE, HAVE, DO, DID, WAS...
Tenses
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Difficulties of the Passive Form
Active => Passive voice
Many tests on Active, Passive voice and mix of them
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Present Simple
Present Continuous
Present Continuous or Present Simple
Many tests on Present Simple, Present Continuous and mix of them
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Past Simple
Present Perfect
Present Perfect or Past Simple
Present Perfect Continuous
Present Perfect or Present Perfect Continuous
Present Perfect Continuous or Past Perfect Continuous or Future Perfect Continuous
Past Simple or Past Continuous
Past Perfect
The pasts
Many tests on Present Perfect, Present Perfect Continuous, Past Simple and mix of them
Many tests on Past Simple, Past Continuous, Present Perfect and mix of them
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Future Simple
Future in Present Continuous (Be going to)
Present Continuous (Be going to) or Future Simple
Future Perfect
Future Continuous or Future Perfect Future Progressive or Future Perfect
Future Tenses
Will and Would: a little further
Future in the past
Many tests on Future Continuous, Future Simple, Future Perfect and mix of them
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Gerund
Gerunds or Infinitives
Infinitive clause
Infinitive in sentences
Infinitive phrase
Many tests on Gerunds, Infinitives and mix of them 1
Many tests on Gerunds, Infinitives and mix of them 2
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For and its use in English
For, During, While
In/into - On/onto
About/At/For/To
At - In - On
Prepositions of time
Prepositions of location
Prepositions: Finding one's way
Prepositions (for / in / of /on / to)
To or For
To - For
at/of/on/to
Verbs and prepositions 1
Verbs and prepositions 2
Verbs and prepositions 3
Verbs and prepositions 4
Verbs and prepositions 5
Verbs and prepositions 6
Verbs and prepositions 7
Phrasal verbs: GET
Phrasal verbs: GO
Phrasal verbs: PUT
Phrasal verbs: TAKE
Phrasal verbs: TAKE, LOOK, GET
Many tests on Prepositions, Adjectives, Phrasal Verbs
Many tests on Particles, Phrasal Verbs
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Adjectives -ing and -ed
Many tests on Adjectives
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Adverbial Clauses
Adjectives and adverbs
Many tests on Adverbs
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Can/Could/May... Must/Have to...
May, Might, Should
Can, Could and Be able to
Modals in Present tense
Modals in Past tense
Modals in Future tense
Must have or Had to
Many tests on Modal Verbs
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Participle Clauses
Many tests on Participle Clauses
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COUNTABLE AND UNCOUNTABLE NOUNS
A (An) or The
Countable nouns with A/An and Some
The or nothing
Using The or nothing with nouns
Many tests on Articles
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Conditional clauses
Conditional and hypothesis
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Quantities
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Find the correct tense
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Placement tests
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Frequent mistakes
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Find the words
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Do or make
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Conjunctions
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Grammar
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Negation
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Participles Placed Just after their Noun
Participles used as adjectives before and after nouns
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Grammar exercises and articles for Reading and Writing
Building a sentence
Fun Easy English
Collection of free English learning resources
English articles
English The Easy Way
Linguaholic
Discuss Cooking
ArtForums
EnglishForums
The Free Dictionary forum
Writing Practice Worksheets
Learn American English online
50 websites for free learning

Talkenglish
Patterns to memorize

For grammar error we can use grammar checker tool too.