The short answer
Recruit 3–5× more readers than the reviews you want, start 6–8 weeks before launch, and send the book 3–4 weeks out. Roughly 20–30% of ARC readers actually leave a review, so if you want 20 reviews on launch day you need 60–100 readers. Almost every disappointing launch traces back to those two numbers being wrong.
Where the readers are
Your own audience is worth more than every platform combined. An email list of 200 people who chose to hear from you will out-convert a thousand strangers. If you have any list at all, ask it first, personally, and ask specifically — "would you read it and leave an honest review in launch week" converts far better than "here's my book".
Genre reader groups on Facebook and Goodreads are where readers actively volunteer for advance copies. The rule is to participate before you ask; groups can spot a drive-by recruitment post instantly, and being useful for a few weeks first changes the response completely.
BookSirens and BookSprout are the practical paid options — modest cost, readers who opted in, and reporting that tells you who actually read it. NetGalley is powerful for non-fiction, library and trade reach, but genuinely expensive on your own; co-op listings share a slot at a fraction of the price and are how most independent authors use it sensibly.
The rule that costs people their reviews. Amazon removes reviews it believes were incentivised. You may give the book away free for review; you may not offer anything else in exchange, you may not require a positive review, and reviewers should be told to disclose that they received an advance copy. Never pay for a review. A removed review can take the reviewer's account with it, and the pattern can flag your title.
How to brief them so they actually deliver
Most ARC readers don't refuse — they forget. Give a specific date rather than "whenever suits", send one reminder the week before launch and one on the day, and make leaving the review as close to one click as possible with the direct link. That alone typically doubles conversion, from around 15% to over 30%.
Be explicit that you want an honest review. It reads better, it's the only compliant ask, and in practice a handful of four-star reviews makes the five-star ones more credible rather than less.
Turn the good ones into a street team
The readers who reviewed on time and wrote something thoughtful are the beginning of a permanent asset. Twenty or thirty of them, kept warm between books, means the next launch starts with reviews on day one and no recruitment at all. That's the real prize — the first launch is expensive precisely because you're building the list you'll reuse forever.
Reviews are one part of a launch. If you'd rather hand the whole thing over, launch and marketing covers recruitment, distribution and the launch-week follow-through, or start with the free 2026 cost report to see where launch spend actually goes.