So I will start by saying I am by no means an expert, however, I have managed to pick a few things up along the way!
I asked over on my page about what you wanted to know or any tips and I got some really interesting questions. Before I jump into them a point to note about Bookstagram (and instagram in general!) is it's a social site - instagram loves if you connect with others, like posts, comment, save, share - go wild! But also follow other accounts! There's an unspoken 'rule' on social media that you should be following less than you follow and I think that is ridiculous! Follow accounts you love regardless of how many followers they or you have!
Okay onto the questions...
Should I wait until I have perfect pictures to start bookstagram?
Absolutely not! Everyone hats start somewhere and the more you take and post the better you'll become. I also only use my phone (I have an iPhone 11) and I think it's fine! I have sometimes used my Canon DSLR but I always prefer my iPhone pictures! (I bought the camera to use on holiday way before bookstagram so definitely not a necessity)
How do you get all your posts to look similar with different book covers?
I use Lightroom (it's a free mobile app or is included in the Adobe software suite which is £9.99 a month.) and I always use the same preset - occasionally tweaking the brightness if necessary. Shameless plug here because I actually sell my preset on etsy but you can use any you like or even create your own!
How do you blend aesthetic with honest recommendations and reviews?
This is tough because we can all be drawn in by a pretty cover only to find we don't enjoy the book! Number one is obviously don't lie, if you don't like something don't pretend to just for a post. That being said - do not tag authors in bad reviews, by all means share your opinion with your followers but the author didn't ask you to slate them and they probably don't want to read it!
On the other hand what do you do if you love a book but it has a cover you really do not want to post? I've included a few examples below but you can always turn the cover back and use the title page, put it under another cover in a jumble, put it in a stack and show the spine, and props are your best friend.