You have some options here, but the first thing you have to make is a decision:
Do I want to help this person write better questions, and learn how to help themselves?
If the answer to that is yes, then:
Point out specifically what is lacking in the question, as politely as you can. Try to be encouraging when possible, the down votes that the question is likely receiving tend to sting. Make the comment as immediately actionable by the user as possible by relating it directly to the actual problems in the question.
Edit the question to fix anything that you can. It's rare that missing information is the only thing wrong with a question. Show the user through action that we take ownership as a community in all of the content that we curate.
Watch out for quicksand - don't let the user make it your responsibility to improve the question. You're there to coach and help, not do their work. If you must exit - do so, but do so politely.
Boilerplate well worded comments can be used, but it's generally good to tailor them a little so they engage specific parts of the question. Otherwise, it looks like someone, well, left a boilerplate comment. While somewhat helpful, that's not very engaging. The more specific you are when you point out issues, the more likely the user is going to be to understand and fix them. If you want to help the user, you need to engage them, not just type at them.
Finally, you can still link to
whathaveyoutried.com, provided that you've given some additional context with the link.
If you don't have the time, inclination or patience to help the person, then avoid commenting altogether. As Yannis points out, this doesn't say anything bad about you. Just use your flags and votes and contribute positively on other questions.
Just try not to feel the need, or at least resist the urge to jab the author of the question for asking a poor question. Remember, leaving a comment to help a new user is supposed to be just that - help, not a whitewashed way to show your dislike for the question that they asked.