I have several hundred hours as PIC in real aircraft, and I have used X-Plane and Microsoft FSX. A few others as well (Janes simulators, etc). X-Plane's physical modeling is more realistic than anything else I've tried, so I would recommend starting right there: Get the most realistic simulator you can, and that's X-Plane.
Get a proper yoke and set of rudder/brake pedals. (Not just brakes, like for a driving simulator. It has to be set up for aviation, and include rudder and toe brake functionality.) This will set you back well over a hundred bucks, but if you're serious about learning to fly, don't waste time on joystick/keyboard/mouse nonsense. As a pilot, you need to "step on the ball" (constantly modulate the rudder to point the nose into the wind). Hitting keys on the keyboard to do this is stupid and will not give you any useful muscle memory. A proper aviation yoke will have things like throttle and prop levers, switches you can map to flap and gear, etc. It's really easy to ignore the rudder in a sim, whereas the airplane will feel weird if you ignore that necessity in real life. You ESPECIALLY need rudder discipline when taking off and landing.
Don't use the flying camera/3rd-person view/etc. Keep the camera in the cockpit at all times.
There is an old saying that practice makes perfect. This is dangerously wrong. The saying should actually be, Perfect practice makes perfect. For this reason, you should stop using your flight simulator until after you start taking lessons. There is no point in learning (or reinforcing) a bunch of wrong stuff, and then having to pay that much more money for your instructor to fix all the stuff you thought was right, at $100+/hour.
This will give you more motivation to actually start your lessons.
I also agree that flight simulators are terrible at simulating talking to ATC. In the real world, you will feel pressure to "do it right" that doesn't exist in a simulator. You will practice this a lot with your instructor. A simulator will never approach all the nuances of actual radio talk. You can only learn that by doing it in reality.
When you start training, you should get a copy of the pilot's operating handbook (POH) for the aircraft you rent. It will have V-speeds. It will tell you how fast you should be going when you rotate, how fast you should be flying on approach, and what your flap settings should be. Whenever you fly in the sim, adhere to these. When doing pattern work, your instructor will tell you what altitude and speed you should be flying on downwind. Do your best to nail this in the sim. Watching your altitude and vertical speed are one of the primary tasks you will undertake as a pilot, so get good at that. (No, your instructor won't let you use autopilot - assuming your aircraft even has one.) In a sim, you can just wander around at whatever altitude. In the real world, you are expected to follow the ONE rule (look it up) while flying VFR, or at an assigned altitude if ATC has given you one. They will be pinging you constantly with radar, and they will expect you to keep it flying level, at a single altitude. You should also be doing this on your own, in areas without radar, simply for the safety of yourself and other pilots.
Practice trimming the aircraft. Whenever you increase or decrease speed, you will have to adjust the trim to keep the altitude from wandering up or down.
You have to keep your head on a swivel to watch out for other aircraft. It has happened numerous times that I had to perform maneuvers to get away from other pilots who were flying at the wrong altitude for their direction (ignoring the ONE rule), happening to cross my path at an appropriate altitude, hot-dogging, bumbling around because they didn't read an airport's approach procedure, not talking on the radio (because the pilot is extremely stupid), etc. If you're lucky, and you're on flight following/talking to a tower/flying IFR in a radar-controlled area, the controller might see that someone's going to crash into you and give you a heads-up. You can't expect this to happen all the time. Someone's transponder might be off, the controller might be busy with something else or have a brain fart, etc. If your airplane has a TCAS, or your flight school will let you rent one, definitely go for that. It's worth it!
Flight sims generally won't punish you for not keeping your head on a swivel. Be aware that in the real world, you have to worry about these situations. I guess you could get an Oculus Rift or something like that, and just get into the habit of looking around all the time.
In a flight sim, you can just fly to any old airport, line up with the runway, and land "straight in." In the real world, it will be one of these three things:
- Landing at uncontrolled airport (VFR): Get on the unicom frequency while still miles away, and follow the approach procedure published in the AFD. This will usually involve joining a traffic pattern. Some airports (like Big Bear in California) will expect inbound and outbound traffic to fly at SPECIFIC altitudes. Don't be a chump and ignore the AFD. Read the approach procedures BEFORE you plan on landing anywhere. It could literally save your life.
- Landing at towered airport (IFR or VFR): Tune into the AWOS or ASOS (published in the AFD) to get the weather and runway condition stuff. It will be announced with a letter (A=Alpha, H=Hotel, etc). Switch to the tower frequency, and say "(airport) Tower, (aircraft name) (tail number) inbound for landing on runway (x) with information Hotel." They will tell you precisely how to land, and on what runway.
- Landing IFR at an uncontrolled airport: Mix of the above 2. An approach plate will tell you how the approach works. You will generally land straight in if under IMC. Otherwise, it's common for pilots to cancel IFR and land as they would VFR.
X-Plane will let you do all that stuff, although the part where you talk to them is automated. It's not bad to practice, so you can get a rough idea of how it's done, but the real world is more subtle and complex. Practice is how you get good at that.
If you're serious about this, get an account at the AOPA forums. You have to be an AOPA member, of course, but it's really worth it. Great resource for student and regular pilots.
EDIT: Commenter below recommends VATSIM for practicing ATC. This is a VERY good piece of advice! Definitely go for that if you want to practice talking on the radio.