A while ago I did a post in my journal
trying to list helpful links concerning Insanejournal.
Right now there are links about:
basics (for example searching the FAQ, ToS and sitemap), insanejournal (settings and viewing options), rss feeds, client(s), abuse (how to report abuse and protect your journal from harassment), mood theme, to-do-list and posting via email.
I'm going to update the list regularly.