Articles

Here you can find the document on articles along with the key for the exercises.

Relative, -ed and -ing clauses

Here you can find some exercises on relative, -ed and -ing clauses along with the key.

Four sources for audio and video streams

Here you can have access to the NPR of the NYC region.  It could be useful if you want to improve your listening comprehension of American English.  You can listen to the live FM broadcast or go to their show archives.  I personally like Radiolab, Selected Shorts and Fresh Air among the shows they air.
 
Here you can have access to the BBC website, which also airs on the WNYC in the mornings Brussels time.  It could be useful to improve your listening comprehension of British English.  They also have links under "Learning English", where you can find numerous tools for learners of English as a second language.
 
Here you can have access to the audio and video streams on The Economist website.  This again is a good source for improving British English listening comprehension.
 
Here you can have access to TED which is a good source for numerous talks on a very wide range of topics.  Most talks are given by Americans and Canadians, but there are also other speakers of different nationalities, including some British.

Position of adverbs

Here are the main rules and exceptions on the position of adverbs in sentences:

First rule: if there is only one verb in the sentence, the adverb comes before the verb as in the following example: He usually comes to work on time.
Exception to the first rule: if the only verb in the sentence is 'to be', the adverb comes after the verb as in the following example:  He is usually on time.

Second rule: If there is more than one verb in the sentence, the adverb comes after the first verb as in the following example: He has already arrived at work.
First exception to the second rule: if the first verb in the sentence is an auxiliary verb with 'to', i.e., have to, need to, ought to and used to, the adverb comes before the first verb as in the following example: He usually has to start working by 9:30 AM.
Second exception to the second rule: if the first verb in the sentence is a contracted negation, the adverbs 'probably', 'possibly' and 'certainly' come before the first verb as in the following example: He probably won't come to work on time.

These being the main rules and exceptions, there is more to this topic.  You can find more information on this webpage, which also provides you with some exercises.

Here is another document with exercises on the same topic.  You can find the key for the exercises here.

Gerund vs. infinitive

Numerous exercises on gerund vs. infinitive along with their key are hereby made available for you to have access at your convenience.  You can also find the list of verbs used with gerund and/or infinitive here.

Here you can find more information and exercises on the same topic.

Conditionals

Here you can find some information and exercises on conditionals.

Here you can find information and exercises on the same topic along with the key for the exercises. (Source: English Grammar in Use. Intermediate by Raymond Murphy)

Here you can find more mixed exercises on conditionals as well as other linking words that can be used in conditionals. There are also some exercises on expressing wishes.

Telephone conversations

Here you can have access to the BBC webpage on telephone conversations.
Here you can find more material on the same topic.