Well, before thinking about any genres, you need to learn the basics. These will be the same for a platformer or a Simulation. Game Loop, 2D / 3D Navigation, how to use engines / how to create your engine from scratch, handling player input, and so on....
Common advice is to start with small easy 2D Games before starting increasingly more difficult projects, so that you learn the topics involved bottom up, you get to finish projects which helps both motivation and building up a portfolio for future use and never bite off more than you can chew.
If you want to ditch the basics and start running before you can walk (not advisable, but people and the amount of challenges they can take on at the same time differ), as Hodgeman said, you need to be more specific.
Are we talking about Flight Sim, Race Sim, Economic Sim, Military Shooter Sim, Tank Sim, THE SimS? Are we talking 2D or 3D? What is your Scope - just a small Sim (like driving through the mud in your backyard) versus a big Sim (recreating the whole City of London for a Drive Sim)? Are we talking simplified Physics or full Physics support?
In the end, what most people understand as a sim today is just a game with very deep and complex game logic in ONE CERTAIN AREA. A Drive Sim is not much different from a current Arcade Racer in most aspects. Both will feature topnotch graphics (a lot of the arcade racers include an abundant amount of details like damage to graphical models even though there is no real damage model influencing the game logic), both feature the same physics and game logic - just in one case logic and physics have been tweaked for a realistic result, while in the other they are tweaked purely for fun (therefore some parts of the game logic have been cut out or simplified.... not many people like driving around in a damaged car, even though its realistic that this car will not go at top speeds anymore and the steering will be difficult).
So if you want to do a driving Sim, I would look at tutorials for arcade racers.
