Take your idea, and write it down on a piece of paper or somewhere where you won't lose it. If you're anything like me, your first idea is so advanced and over-the-top that it is near impossible for you to create it as your first game.
There are a lot of tutorials out there, but a lot of them are subpar and assume you have a basic knowledge of programming already. I suggest you read up on some of the simple aspects of programming: stuff like variables, functions, constants, etc. These concepts are pretty much universal among all programming languages.
Once you've done that, look up an AS3 tutorial like this one and you're on your way.