How to Give Good Advice

Sometimes people will come to you for advice because you're an expert, or at least more of an expert than they are. In that case, you can simply tell them "keep a reserve of cavalry back here" or "clean it with mild soap and water first" or "if you get a retroencabulator, make sure it has a malleable logarithmic base"; if you're an expert, there's a reasonably good chance that they'll listen to you.
Sometimes, however, they come to you because you're a sympathetic (or captive) ear, and you see they're doing self destructive and are just too caught up in their situation to see it. Generally if you just come out and bluntly and directly say "You should: stop huffing methane | file bankruptcy | throw out that useless leech of a boyfriend | get at least a GED | not vote for Obama", it doesn't go over too well. What works better is to ask "If your friend or coworker was in that situation and asking for advice, what would you tell her?" They'll pause for a couple seconds, and then come out with the same advice you would have--but since it's them saying it instead of you saying it, they won't be offended at you.
I grant you that having dispensed this good advice for themselves, they still won't follow it--but you can't have everything.