English Grammar Online 4U is an excellent writing resource that provides a lot of very useful tips without getting too complicated.  Their General Information on Writing English Texts is a very good place to start improving your writing.

It may not always be necessary to use phrasal verbs, but they are a big part of using English naturally and fluently.  So how do you practice them?  First we need to figure out what exactly is difficult to remember about them and then find a way to isolate that and drill it in a way that we can remember.  Read my blog post about remembering phrasal verbs if you haven’t already.  Once you have examples that you want to practice, Anki is...

One of the best resources for this (besides a good monolingual dictionary) is Using English.com.  Using English has an excellent phrasal verb dictionary (also an idioms dictionary) as well as a forum where you can ask for extra information or just check that you are using them correctly. Try and notice patterns with certain particles (the prepositions or adverbs that make up the phrasal verb) and how they change the meaning of the base verb on...

Sometimes an exercise book just isn’t enough and you really want to know the details.  This is when you need a grammar reference.  Practical English Usage and Cambridge Grammar of English are two of the best.

Raymond Murphy’s Grammar in Use Intermediate is one of the most comprehensive books around of grammar rules and exercises.  Every student should have this.  There is also Advanced Grammar in Use, and while it is very complete I think it is appropriate for an extremely high level (Cambridge Proficiency Exam).  A good exercise book in between these two is Cambridge Grammar for CAE and Proficiency.