There is much to be said here. There is a lot of advice out there. Feel free to add your own good sources or annotate some of these.
Pat Thomson's blog is an excellent resource about academic writing in general. Well worth browsing back through older posts.
Inger Mewburn, better known as the thesis whisperer runs an excellent blog that also is well worth perusing earlier posts. For example, she has an excellent piece on How to use deliberate practice to improve your writing. She also has an excellent verb cheat sheet that offers useful advice about how to convey what other researchers are arguing or not.
For a delightful and informative collection about reading, writing and a lot of other stuff, the blog that Maria Popova maintains is well worth a look around.
There can often be a conservativeness in the advice you receive about writing. As Helen Sword's recent book1 argues, much of this is misplaced. There is also some confusion about the use of 3rd person passive in writing. In days gone by, the 3rd person passive reflected a kind of science-aping in the social sciences, i.e. our writing is as detached as that of a scientist. If you come across people who insist on you writing using the 3rd person passive it will be worth exploring their reasons (carefully). The fact is that the vast majority of science journals use first and third person where appropriate and accounts are written in active voice, not passive. Passive voice has a role but it is for style, not to convey that somehow the author does not exist or that if you write in active voice that somehow you will convey a lack of objectivity. A useful account of these arguments can be found here. Helen Sword offers an account in her book:
Once upon a time, PhD students across the disciplines were taught that personality should never intrude upon scholarly writing. Apprentice scientists, social scientists, and even humanities scholars were warned that their research would not be taken seriously unless they reported on their work in a sort of human- free zone where I and we dared not speak their names. Some academics, forbidden to say I, resorted instead to the royal we (“in this paper, we [the solo author] will argue”), the inclusive we (“from these results, we [the author and readers] can surmise”), or awkward, third-person constructions (“this writer has argued elsewhere,” “the present researcher has found”). Some took on a godlike persona, surveying the research landscape from on high and delivering subjective pronouncements in adverb-inflected language that cleverly disguised opinion as fact (“cleverly disguised opinion as fact”). Some let their research stand in as a kind of proxy for the absent I (“this paper will argue,” “this example demonstrates”). And some twisted their sentences into passive verb constructions that hinted at but never acknowledged personal agency (“it can be shown,” “the research was performed”).
So, bottom line, the best that can be said about people who insist on or encourage 3rd person passive is that they are living in the past.
Helen also offers an online test for your text which will provide a useful analysis for what she terms flabbiness of texts! :) Give it a try. It can be quite handy. There is also a post of hers on the conversation, seven secrets of stylish academic writing.
Jo van Every also keeps a blog site that is a useful source of advice, ideas and resources.
Another useful blog, explorations of style, is maintained by Rachael Cayley from the University of Toronto.
Many accounts seem to suggest that writing is a tidy activity. "We" all know, however, it ain't like that. There is a lovely account by Ninna Meier on on the materilaity of writing in academia or remembering where I put my thoughts2 in which she explores the messiness and materiality of writing.