What is the best way to continue to learn grammar at an advanced level?
Five short answers:
1. Learn as much as you can from practice and experience rather than text books
2. Keep your own examples and observe patterns (and exceptions) in the language
3. Focus on particular areas which give you difficulty (eg. articles, relative clauses)
4. Learn as much as you can from any feedback you get on your written English
5. Remember that almost every grammatical 'rule' is likely to be breakable in some situations (so don't become slave to rules!)
As English becomes more of a diverse and international language it is less and less possible to point to an authority and say 'that is the correct way!' (or 'that is a mistake!').But there are of course general conventions for British and American English grammar which you need to know.
For reference, I would recommend Advanced Grammar in Use (Second edition 2005) by Martin Hewings (Cambridge University Press, http://cambridge.org/uk/, ISBN 0521532914 with answers). This book covers grammatical points in an imaginative way, giving examples and practice exercises on facing pages. Also has some useful summaries at the back. If you buy this book for self-study, make sure you get the one with the answer key!
For more practice exercises, try Advanced Language Practice (Second edition 2004) by Michael Vince(Macmillan Heinemann, http://www.macmillaneducation.com/ , ISBN 0435241249 with answers).
Online grammar resources can be very mixed in quality and scope. I would recommend the OWL (Online Writing Lab) at Purdue University for guidance on grammar and writing at http://owl.english.purdue.edu. Go to 'Handouts and Materials' for options.
For some useful quizzes on English grammar, donated by teachers, see http://a4esl.org/ (uses mostly Java and Flash).
I would also strongly recommend the pages on tenses at Englishpage.com. All the tenses are explained clearly and there are online practice exercises for each one. See http://www.englishpage.com/verbpage/verbtenseintro.html.
For questions on usage you might try the vast Alt. English Usage at http://alt-usage-english.org/index.shtml. This is searchable and very good for settling disputes over usage, such as: ‘Do we say ‘different from, different to or different than?'
More grammar guides are at the US Webster University site http://webster.commnet.edu/grammar/index.htm where there is also an online text book on writing called 'Sentence Sense' at http://webster.commnet.edu/sensen/index.html.
A teacher, David Tillyer, has produced a useful summary of a tricky area - gerunds and infinitives - at http://www.geocities.com/gwyni_99/gerinfless.html. He also offers a list of verbs and practice tests.
