Henry V1, parts1, 2 and 3, are generally considered his earliest successes, vying with The Two Gentlemen of Verona, as, perhaps, his first work. Nobody knows, of course, but he was 'contributing', to other plays by other playwrights, in his 'apprenticeship ' to writing. That way, he learned the rudiments of stagecraft, dialogue, juxtaposition and rhetorical delivery, so much so, that he was able to put together a sort of play, (The Two Gentlemen of Verona), which is awkwardly constructed, Shakespeare being unable to balance out the play when more than four people are on stage together, and geographically incorrect, (Valentine leaves Verona for Milan by boat!), etc. Nevertheless, from that experience he learned quickly, and his successive efforts where much more rounded and sophisticated.