If you've been to any PHP conference (or attended a PHP-related online event) in recent years, you probably have heard of the speaker/event feedback site Joind.in. The concept is simple: when you attend a talk or event you go to the site, give the speaker a star rating and leave them comments. This gives the speakers direct feedback on how they did and where they can improve. There's a a trick to giving valuable feedback, though, and Joshua Thijssen has posted some helpful tips to guide you and your comments in the right direction.

The joind.in website can be considered a presenter’s portfolio: it contains a list of talks they have done in the past (and where), plus it contains reviews from attendees. [...] This is why many conferences and presenters will talk about joind.in and ask you to rate and comments on their talks: it gives them feedback on how you experienced the talk, what can be improved to make it even better, and gives the presenters more chance to get accepted on even the larger conferences, where sometimes there are only 50 slots, but over 500 people submitted talks).

[...] Even though commenting and rating talks by itself isn’t really difficult and is quick to do so, there are some common “mistakes” and pitfalls which I’d like to discuss.

He breaks it down into five main points, elaborating on each as he goes through them:

1. Stars don’t tell you everything
2. Rate the presentation and speaker, not your expectations.
3. Don’t punish the presenter for external faults
4. Comment anonymously
5. Give suggestions on how to improve

For each one he also gives examples of good feedback versus comments that aren't as helpful to the speaker. Each one of these is an easy trap to slip in to, so remember them next time you're giving a speaker feedback (even if it's not on Joind.in!).