I've been teaching ESL for a short while now. I'm fluent in four languages, and am no stranger to the language-learning process. However, as English is my first language, I don't have the same intimate knowledge of problem areas, "a-ha!" moments and mnemonic devices that I do for say, French. Textbooks provide this sometimes, but they aren't always perfect: for example, it was only after I had already memorized and gotten used to which verbs in French take "être" in the passé composé that I realized these were generally verbs of motion.
Essentially, what I am asking is:
Non-native speakers of English: what little "tips and tricks" have you found especially useful in your English studies? What areas of English do you find particularly difficult? What have your instructors done that really helped you? What have your instructors done that have been generally useless or aggravating? What (preferably online and free or low-cost) resources have you used to supplement classroom instruction?*
For example: I tell my students to think of "could" as both the past tense of "can" and "would + can," something I reversed from my studies of Romance languages ("could" generally expressed by the conditional of "can") that I haven't yet seen in my admittedly short time perusing ESL textbooks.
Of course, advice from other language teachers and anything else you would like to add is welcome.
It would be appreciated if you could provide your native language, how long you've been studying English and what contexts you've studied it in (e.g., secondary school, language academies, self-study).
*On my students' last days of class, I steer them towards WordReference, Forvo, Urbandictionary and Livemocha - though I don't have much experience with the last one.
Thanks in advance!