Where to start
Begin with the shorter dialogues that dramatise the trial and death of Socrates: the Apology, the Crito, the Euthyphro. They are compact, they are gripping, and they give you the figure of Socrates who will animate so much of the rest. The Meno is a natural fourth — the standard introduction to the Platonic claim that virtue is in some way knowable, and a clean example of the elenchus at work.
After those four, the Symposium and the Phaedrus are the natural middle stops. They are dialogues that do as much philosophically as they do dramatically, and they begin to show what Plato can do at full range.
The Republic is the centre of the corpus, but it is not the right first thing to read. Come to it once the dialogue form is familiar, and read it with the patience the argument deserves. See the companion guide, Understanding the Republic.
What the dialogue form is doing
Plato wrote no treatises. The dialogues are not lectures with a spokesman; they are arguments staged between distinct characters with different stakes. Sometimes Socrates is the principal voice and clearly Plato's; sometimes the figure who appears to lose the argument is doing something the reader is meant to take seriously; sometimes the dialogue ends in aporia — productive deadlock — and that is the point.
The most common beginner's mistake is to read for "Plato's doctrine." The dialogues are doing philosophy, not delivering a system, and they are not always in agreement with each other. The Republic's treatment of poetry is not the Phaedrus's. Some of the late dialogues (Theaetetus, Sophist, Statesman, Parmenides) are substantially harder than the middle-period works and are reasonably left until last.
Stephanus pages
Citations of Plato use the page-and-letter system established by the 1578 Geneva edition of Henri Estienne (Stephanus). A reference like Republic 514a points to a specific passage in any modern edition, because every modern edition prints the Stephanus pagination in the margin. Get used to seeing the numbers; they are the way Plato is talked about.
The standard Greek text is John Burnet's Oxford Classical Texts Platonis Opera. The platform's Sources page lists the open-access archives that mirror it.
Translations
English translations of Plato vary widely in style and accuracy. Older, fully out-of-copyright translations — Benjamin Jowett's nineteenth-century edition is the best known — are mirrored on Perseus and the Internet Classics Archive. They are usable, especially for orientation; their style is Victorian in a way that occasionally obscures the argument.
Modern translations are easier to read but each has its own choices (how to render aretē, whether to keep or domesticate the Greek formulae). When two translations diverge meaningfully on a passage you care about, look at the Stephanus reference and check the Greek; Perseus puts the original and the translation side by side.
What to set aside
Two common modern frames make Plato harder to read than he is.
The first is the picture of Plato as a system-builder whose dialogues are veiled treatises. Treat each dialogue as the argument it is; notice where the arguments cohere and where they do not. The unity is real but it is the unity of a body of work, not of a textbook.
The second is the modern political reading that takes the Republic as a manifesto for an ideal regime to be implemented. The dialogue itself treats its proposals as deliberately extreme thought-experiments designed to make the soul-city analogy visible. Be careful before attributing to Plato what he writes as a hypothesis.
What to take with you
If a phrase keeps recurring in a dialogue, take it seriously. If a character is given more sympathy than the argument allots them, ask why. If the dialogue ends without resolution, do not assume Plato failed to solve it — assume he meant the question to remain open. Reading Plato well is, in the end, learning to read with the same patience the dialogues themselves practice.