The best way to start developing a video game is to not start developing a video game.
Video games should be completely planned out first before you begin developing it, or else you are pretty much guaranteed to never finish it. Creating a video game is a massive undertaking that can take years. If you go into it without having an incredibly well thought-out vision, you will likely end up ditching the project.
Plan out exactly how you want the game to work, draw pictures of exactly how you want the game to look, write out detailed explanations of the game's mechanics. If the game has a story, write out the entire story.
Remember that a good game isn't just programming. You also need art and music. If you are not an artist and a musician, make sure to find some.
Once you have all that done, then you can start looking into actually developing the game. Unity is the most popular game engine. It has quite the learning curve, though. Something simpler for a beginner like Game Maker could also be used. If you have experience programming, making a 2D game from scratch in something like Java or C++ isn't very difficult, but if you lack experience, you'd probably want to stick with a game engine like the ones previously mentioned.
Since game engines have learning curves, you'll want to spend a decent amount of time learning to use the engine before making a game. Follow a bunch of online tutorials and create a bunch of scratch projects on the side to make sure you know what you're doing.
