The phrase "my first effort" is correct and can be used in written English.
It is often used to describe someone's initial attempt at something or their first try in a particular task or endeavor. Example: My first effort at baking a cake turned out to be a disaster, but I didn't give up and my subsequent attempts were much better.
My first effort backfired a bit.
"My first effort was vile," she recalled.
My first effort was a classic raspberry, which turned out to be so surprisingly delicious that I felt as if I'd broken some secret code.
But it was my first effort, and I've made 17 full-length films since, as well as having written and directed a dozen or so stage plays, including Abigail's Party.
The results are amazingly good for such an easy recipe: rich and creamy, with a lovely flavour – but it still lacks the elusive caramel tang of my first effort.
My first effort, made early one morning inside the eighty-sixth-floor observation deck of the Empire State Building — under the tutelage of the third man on the crew there, Ron Zeibig, an affable hulk with stringy blond shoulder-length hair and a black belt in jujitsu, nicknamed Thor by his last partner — was not a success.
Looking back, my first efforts were overambitious and inconsistent.
This led me to focus my first efforts on the adidas dataset.
I graduated to puzzle construction a few years ago with my first efforts showing up in such celebrated publications as a philosophy midterm given by a professor friend of mine as well as my company's in-house newsletter.
My first efforts were prose superhero stories for the comic-book fanzines of the 60s, but I soon moved on to sword-and-sorcery tales and mysteries and SF, and started dreaming about making a career as a writer.
My first efforts were to no avail, so I eventually resorted to a slightly more aggressive attack.
