My answer on 2/26/19 to someone asking "where to start reading?"
How much background in philosophy in general do you have? We can fine tune the suggestions much better if we know that. In the meantime I want to say that in my view the best book for a person new to philosophy to read is Norman DeWitt's "Epicurus and His Philosophy." Don't pay an exorbitant price for it - any library has it, and you can buy digital versions for a reasonable price, and if you search hard enough you can find PDFs online.
Another excellent free online source is Frances Wright's "A Few Days In Athens," which is a fictional story that does an excellent job of introducing someone to Epicurus (that is in fact the theme of the story - introducing a new student to Epicurus). https://l.facebook.com/l.php?u=http%3…D20frGAxNzYhgfP
I don't have the time to develop this point as I would like to at this moment, but I want to stress that unless you are recently arrived from Mars, you are going to bring with your reading of Epicurus many preconceptions which need to be put aside in order to judge Epicurus fairly. The dominant philosophy of the world today is a mishmash of stoicism / platonism / aristotelianism / judaism / christianity which is virtually inescapable. You are conditioned to view all issues through that lens, and most people see what they expect to find when they are reading Epicurus.
The advantage of reading A Few Days In Athens or DeWitt's book is that both sources explain the background of the issues that were present in Epicurus' day, and how he answered them.
Unless you read a work like that, which explains the situation, it is very difficult to get a balanced picture by going straight to the letters of Epicurus, or even to Lucretius, which is a much longer and therefore more thorough presentation.
An excellent test for whether you are getting a balanced perspective is the treatment given by a writer of Epicurus' views on pleasure. If you come away with the idea that the writer is telling you that pleasure is nothing more than the absence of pain, and that the best life is therefore gained by suppressing pain in any way possible, and that the simplest life is always the best, then you should look elsewhere (to DeWitt or Wright) for a more balanced perspective.
Another excellent test is to look for how many references a writer makes to "pleasure" in discussing Epicurus. You will find that writers who are ultimately some version of Stoic will de-emphasize the word pleasure, and talk mostly about "happiness" or "ataraxia" or even "flourishing" -- and these writers too are perverting Epicurus to fit their own perspective of the best life.
There are many good books that have many excellent points about Epicurus, and I specifically include Hiram's book and Haris' book (both members here) as good for practical application of the full theory. But neither of these attempt to provide the full sweep of the theory in a manner that an ancient Epicurean would probably approve, and you won't get in English anywhere but DeWitt, and to a lesser extent from Wright.