Reviewing another author’s book and politely requesting a review for your own is one of the BEST things you can do to gain a little more attention.  

I don’t know if there’s a "Reviews Etitquette" thread on the forums somewhere, but I personally try to stick to the following (these, again, aren’t official rules in any capacity, just what I personally tend to think):

1- If you don’t have something nice to say, don’t say anything. While it’s true an author can disapprove of your review and not post it anyway if it’s really negative, you want to try to find SOMETHING that was working and focus on that. Writing style, character development, good choice of words, interesting setting, mind-boggling premise, etc. etc.

2- If you DO have something ’negative’ to point out, do so in the excerpts/comments alongside the chapter itself. (You highlight the text/quote with your mouse and a message field SHOULD pop up, sometimes it doesn’t - so then just click on your highlighted section.) Don’t be negative though... Be CONSTRUCTIVE in your comments. Point out what’s wrong and explain why it’s not working, with a suggestion for how to improve it. We’re all learning here, people! :D

3- Keep the review short and sweet. 4-5 sentences. Leave some other room for other reviews! I don’t know about you, but I’ve never finished reading a long review for a book around here. But I’ve read a thousand short ones.

Back to point #1... I don’t know if it’s openly discussed around here so much - but yes, in real life, there ARE such things as negative reviews. Why discourage real life from taking place by encouraging only positive reviews? I think it has a lot to do with the nature of crowd-funding. On a typical kickstarter page, you won’t find a single sentence dedicated to reasons NOT to support a project. Likewise, I think it’s important for an author to select someone else’s experience that help to highlight the benefit of reading their story.  Like I said before, it’s okay to find a bunch of negatives, but keep them out of the review. You’re trying to help a member of the community get the word out on what their book does well, otherwise what’s the point of you taking that much time to read their work and review it?

..........All that having been said, I wouldn’t mind exchanging reviews. :D I can do probably one per week, considering my current workload.