By avoiding made-up words like "adviceful." Try to put yourself in the asker's shoes, and determine what type of answer you'd like to receive if you were them.

Here are a few general things to keep in mind:

Be polite

Take your time and think it through

Good spelling and grammar help a lot!

Do not curse

Don't use all capital letters - people will think you're "yelling"

If it helps illustrate your point, include an image or a video

Don't just say "I don't know" or "If you do a search, you can find the answer" - It just isn't a very helpful answer, and oftentimes people are asking here because they've already tried to use a search engine and still couldn't find what they wanted.

Cite your sources - people are more likely to believe you if you can back up what you say. The best way to cite a source is to paste the link right into your answer

When giving a link to a page with the answer, also provide a summary the answer. This way, if the site you're linking to goes down, people on Answerbag will still get a good answer, not just a broken link

Stick to the facts - if you can cite specific facts, events, or your experience, your answer will appear more authoritative

Do not belittle the questioner. Everyone deserves an answer!

Be sure to look around at other good answers on Answerbag, and you'll get an idea pretty quickly of what people like to see in an answer, and what they don't!

Tell the truth as you know it to be, you can do nothing else.

Know your subject before giving advice.

With honesty and to the best of your ability... If you don't know about a subject don't give bunk advice!!