On this page, some tips and tricks I found useful, especially when starting in iRacing, but even now, I stumble across little "I wish I had known this much earlier" things. I grouped them as good as it gets, and put them in alphabetical order:

AI

-- Once loaded into the Simulator, on either side of the usual Practice/Qualify/Race button (top center of the screen), you will see a “Prev” button and “Next” button. You can use these to go back to the previous session (for instance to restart after a lap 1 turn 1 disaster) or skip ahead to the next session (to skip from qualification to race for instance).

-- If you are "competing" in an AI season, you can re-run a bad race after it is complete, using the “Re-run Last Race” option to give it another try. If it is driving against the AI, it is not cheating, right? ;-)

Car setup

-- Fixed setup races: don't forget that you can still change the brake bias (this can also be changed during the race).

-- Field Of View (FOV) on the virtual mirror: the default setting is to give you a wide view as possible, but the downside (at least for me) is that cars that are really very close to you, looks much further away in your mirror. If you don't like this, you can change the FOV setting for this virtual mirror. This is probably something that you need to test first to find a good compromise between keeping the overview and having a good sense of proximity of the cars behind. While in the car, press F9: the default seems to be 120 degrees, and it seems many people are lowering it to 83 degrees. Easiest is to test this with a friend in a test session, let them drive really close to you and touching your car: start from here and adjust the settings. You could also test this in the AI I guess.

-- Car setup folder structure: if you have a lot of setup files for one car, it could be a hassle to quickly find what you are looking for. You could add sub folders (via your file explorer) in your car setup folder C:\Documents\iRacing\setups to have this organised better. For instance, if the tire model of that car has been changed, it could be useful to archive the old setups and fine tune new ones. Or you could make a sub folder per iRacing season. Or per event you are in competing. Anything goes.

-- Garage notes: in the garage screen, don't forget there is something called "garage notes". Make it a habit to check if there is any info there, it could give you very useful information about how your car functions. For the newer cars in iRacing this typically contains information on the LEDs on your dashboard: traction control, ABS etc.

-- Change the "look angle". If you are using a single monitor setup, chances are you use buttons on your steering wheel to quickly look left or right when you are in traffic. By default, this is set to 65°, but many people find it less disorientating when lowering this angle to for instance 30°. You can change this permanently in the app.ini file (C:\Documents\iRacing\app.ini): look for cockpitLookAngle and change it to 30.000000.

-- Set the correct force feedback (FFB): drive 2 laps in the simulator, stop and press F9 to open the Graphics Adjustments black box. In the bottom right corner of the black box it should say ‘auto’. If it does not, then you must enable this FFB setting in the Options screen. Start driving again, the iRacing software will automatically set the correct FFB for the car. Note: you can either use FFB settings per car or the same setting for all cars.

Driving

-- Pause your sim in a test session by using the Pause key on your keyboard. Press the Pause key again to resume. Note: sometimes this could break your telemetry logging. What's the difference with just parking your car? Well, all dynamic things like tire temperature changes, track changes, weather changes etc are also paused then.

-- Using the pause key as described above also works during AI races

-- When in a practice session, you could use groups if things are getting too busy for you, or if you just want to drive with your teammates. When in the simulator, click on the entries tab, on the top left corner you can change the group.

-- Use reference (or ghost) cars to compare your driving and set yourself a challenge. You can drive against your own hotlaps, but you could also import these files from other people. These files are in C:\Documents\iRacing\lapfiles\ and then a sub folder per track. OLAP files are Optimal lap files, BLAP files are Best lap files.

PC/video performance

-- Test "Game mode" on Windows 10: many people report that by switching it off, performance in iRacing is better. Depends on your specific setup (full screen or not, etc).

-- In Options screen, Graphics tab: don't use vsync

-- In Options screen, Graphics tab: set the frame rate limit, also test this when you run with a lot of cars on track. Check the fps graphic performance indicators that you could show in the simulator while driving.

-- On your gaming PC, don't run anything in the background, especially not Chrome

Replays

-- Skip quickly to incidents: in replay mode (works also in saved replays), press CTRL + 3 to jump to the next incident; use CTRL + 1 to go to the previous incident in the race. Note: this is about any incident for any car, so not just yours!

-- Enable replay spooling in Options screen, Replay tab. This makes sure that your replay for long(er) races are completely saved

Rookie tips

-- you can move the iRacing overlays (aka the black boxes) by pressing Alt + K. This will unlock their fixed position so that you can move them around with your mouse. Some items may only be moveable by dragging their borders. When you are done, Press Alt + K again to exit and save. Note: this can be handy if you are also using 3rd party overlay tools.

-- you can further resize the black boxes and other interface elements by pressing Ctrl + PageUp or Ctrl + PageDown while in the simulator screen. It does not change the size of the virtual mirror however.

-- Set the correct Field of View (FOV) in iRacing. In the iRacing Options screen, select the Graphics tab at the bottom of the Options window. In the top right corner of that window you will find the FOV settings. Measure the monitor width and viewing distance with a tape measure and enter them into the boxes. The viewing distance is the distance from your eyes to the monitor. The iRacing software will automatically calculate the correct FOV for your display configuration. Make sure these numbers are correct. If the FOV is extremely low, then get closer to your monitor, get a bigger monitor, or get triples. You can increase the FOV a little, but best is to stay within 3° from the calculated value.
Your viewpoint from your car cockpit may seem strange at first, but give it some time to get used to, you will be faster and more consistent. You can Google some instruction videos on this topic and get more explanation why this is so important, but beware, you are entering some religious discussion on the topic ;-)

-- Take a screenshot/record video in iRacing: in the Options screen in the Video section, you have the key bindings for taking screenshots and start/stop video recording. The defaults are Ctrl + Alt + Shift + P and Ctrl + Alt + Shift + V. This creates a screenshot/video with a watermark and iRacing logo in folder C:\Documents\iRacing\screenshots. If you don't like that and want a super high-resolution screenshot, then you can change settings in the app.ini file in the [Video] section. The key bindings for the high-res picture is Ctrl + Shift + Printscreen.

-- Key bindings: in the Options screen, tab controls, you'll see a list of possible actions you can start and how they are triggered. Check which ones are most important to you and configure the key bindings to trigger an action by pushing one of the buttons on your steering wheel or controller.

-- Refresh or reset car paints in iRacing: press Ctrl + R.

-- Disable automatic fast repair, fuel fill, and tire changes during pit stops. Open the file C:\Documents\iRacing\app.ini. using any text editor like for instance Notepad. Look for the section [Pit Service]. Set autoResetFastRepair=0 to turn off the automatic fast repair, set autoResetPitBox=0 to disable pit services like fuel fill and tire changes from happening automatically. Downside of these settings is that you need to set them manually when you will need them (using the F4 and F5 black boxes). Depends a bit on what type of races you race most: setting the default to off is best if you are doing mostly sprint (short) races, whereas for endurance races you want them by default switched on. Note: it is worth to further investigate the app.ini file because here you can change many settings.

Sound

-- In Options screen, Sound tab, set sound to XAudio2
-- On the same screen, you can change the sound level for different kinds of sound: engine, tires, events etc. It's good practice to set the tires sound relatively higher than the other sounds, giving you good feedback what's happening with your tires when turning, braking etc. Vision (FOV) and sound feedback is more important for driving fast and consistently than the force feedback of your steering wheel.
-- Make sure that you know how to mute a driver in iRacing, or even better, mute all drivers. See key bindings to assign the right keys for you.

Tools

-- Crewchief settings you could change: you can fill in your name in the top right corner, for a more personalized experience. Click on properties, and select in the category filter "UI, Startup & paths": now you can change the settings for "Minimize at startup" and "Run immediately". If you like you could also tick the "Use sweary messages" setting, giving you a more, euh, unpolished (and more funny) version of Jim, your spotter.