The Jordanville Prayerbook from Holy Trinity Monastery. Beautiful prayers.
I hope I was helpful. The following is just extra information:
If you're curious about prayer, you could also go straight to the Psalms, one of the books in the Old Testament, a collection of 150 prayers (151 in Orthodoxy) that all Christians (and Jews) use regularly. It shows the various kinds of prayers (petitioning God for something to happen is only one form of prayer among others), and the words themselves show what our purpose is in saying those prayers. But, of course, this is only if you're really curious to know about prayer.
Also, you may want to get a version that has notes, as the book, like much of the Old Testament, can be difficult to understand for someone who's not already in that tradition. Sadly I don't know of a good edition in English - I like the one in the Orthodox Study Bible but, well, you would have to buy the whole Bible to get it.
For something less "biblical" and more along the lines of what a Christian usually prays, you could buy a prayer book. Again, I recommend this one but only because I haven't checked out others in English: https://www.amazon.com/Prayer-Book-Holy-Trinity-Monastery/dp/0884651754/
Of course, again, this is only if you'd like to do some further reading on Christian prayer by going straight to the source. And I only pointed to Orthodox ressources because that's what I know, maybe Catholics and Protestants wouldn't necessarily agree with what's in those books and would recommend others instead.
When I was first "investigating" Orthodoxy, I just looked on Amazon. I actually found this prayer book. It's compact and good for carrying around with you. I have it in my backpack most days. I am still on my journey and have not yet converted, but I read it along with my morning bible reading, or during times of struggle or in need of edification.
Commemoration is always good. https://www.amazon.com/Prayer-Book-Holy-Trinity-Monastery/dp/0884651754 - is also wonderful, and what most Orthodox Christians use.