Apart from these features specific to academic writing, it is of course important to use words accurately. If you're a writer who mixes up words (affect or effect?/ accept or except?) you might find the following site handy:
http://www.wsu.edu/~brians/errors/errors.html#p

If you're unsure about punctuation, check out these sites:
http://ccc.commnet.edu/grammar/marks/marks.htm
http://owl.english.purdue.edu/handouts/grammar/g_sentp.html
http://www2.actden.com/writ_den/tips/sentence/puctuate.htm

Download the document (word doc)

Try this exercise. It will help you expand your choices when it comes to wording your text. See if you can easily think of alternative forms for each word in the table, and add to the list with more words relevant to your writing.