Free books (and on sale <$1.00) are also an incentive and have more often than not resulted in me buying other books from the author.
Serendipity in book stores - not very frequent because bookstores are not close to me. I recently bought 3 books from various bookstores while looking at what was available. One I had been meaning to read for years the other two were by authors I knew of but had never read.
Random Internet reference, I read Stanger in a Strange Land because of the SO answer "You don't grok vi" - I wanted to grok grok.
Travel inspired, I read some Hemingway because I was going to Spain.
edit: Online reviews are like social media comments, bring some popcorn. If I want to read criticism about a book, it will be from a more reputable source. But, that is not to say I won't read a book with bad reviews from a more reputable source. Their negative spin might make me more curious.
In a diffrent age I lived in baltimore, and every day on my way to work would walk past the same homeless (or at least I thought) man sitting behind the church, who would be reading and have a pile of books next to him. One day I passed him and he was exchanging a book with a woman. My curiosity got the better of me and I watched the exchange and listened to the conversation. Apparently, he lived in the church, in trade for cleaning, with his basic needs provided for he had taken up to forming his own little book exchange for tips. After talking with him for a bit, about what I read and what I liked he promised me a book for the next day... Over the course of the next year, I read some rather interesting things that I NEVER would have picked out on my own, and was introduced to them in such a way as to make them much more palatable. As an example I had never been a fan of military history, after throwing a pair of military scifi books my way i got something more factual and loved it.
Because of him, I basically read anything any one gives me... fiction, non fiction, domain specific stuff.
Plus, over the four years we've been doing our little gift exchanges we've created a fantastic library that charts our relationship. If we make it to 50 years together it'll be something to behold. Assuming books are even a thing then.
> Assuming books are even a thing then
Well, they have been "a thing" for close on 2000 years, so I wouldn't hold my breath waiting for them to disappear in the next 50 ;-)
Books are selected per current area of interest. As source of recommendation i use current and past edition plan from scientific publishers.
I dont know anoyone around me who read these kind of books so i dont get recommendations from friends of mine.
From non-scientific literature i read books based on recommendation from HN or other forums like quora. It also depends on my mood.
Always i read something because i wanna learn something new, get fresh insight or different point of view. Side effect is that i can join almost every discussion on various topics. Sometime i also decide if i will read it or not based on future usage of obtained information.
You might be interested in https://mytemp.email. It'll issue you a temporary email address without you filling any form. The email address is accessible by a URI and is perishable (dies if not accessed within 24 hours).
How I find my next book to read? Mostly chance. For example, I regularly visit local bookshops for a browse, and if anything especially catches my fancy, I'll buy it (usually after having read the first quarter of it in the shop). As a student my budget for "luxury goods" isn't phenomenally large, but I do make a point of buying one or two new books a month. Buying a book after a friend's recommendation is rare but not unheard-of. Sometimes reading a review (of the professional, printed in a published magazine type - NOT online user reviews) will also tempt me to buy.
Hope that helps :-)
Goodreads as well.
I see a LOT of book spam on Twitter and Facebook, none of which I have ever bought. Free download maybe, but no purchase.