Which Plato dialogue to read first?
Some tips and ideas.
Are you reading Plato in Greek to learn about style or in Greek or English or your own language to learn about philosophy, literature, or ancient culture and history.
If you're lucky your library has a full set of the Loeb classics or several of the Penguin translations perhaps? Or you've had the time to download some of the older translations available on line. You might want to google downloadable Loebs and you can can e-texts and pdfs of older translations from several sites.
I'm fortunate enuff to have a small but good collection that includes Greek originals and Penguin and other translations however I acquired these new and second hand over three decades.
What would I suggest?
Start off with the Phaedrus or Symposium and the Apology.
Do read the Republic.
Do not fixate on one favorite dialogue.
Read both the major and minor dialogues.
Do not just read one translation.
Different translations may have differing notes or commentaries or introductory essays that can add to your own insights and analysis.
Do not presume Plato is always being serious!
Be aware of the history and politics of Socrates's age.
Even if you are only interested in the philosophical concepts you still need to know about the politics of Athens and Sparta.
Finally whatever your reasons for reading Plato do it with joy and pleasure!
Now go and read some Plato!