• Firstly I think it's important to note that how much we steer to get to the maximum grip point is highly variable and depends on momentary car balance, trying to find optimum steering angle for a car without grasping it's dynamics is a sure way to confusion and slow learning.
Now a car in perfect balance at the best slip angle for the rear tyres will require exactly 0° of steering to corner at maximum grip. Most often cars have understeery balance and that requires some positive steering angle. The more understeer the car has at given moment the more angle is needed.
Car's momentary balance can change depending on driver inputs and car's rotaion (stance):
- Lightly braking creates forward weight transfer reducing understeer and the need to steer. Similarly full throttle can also reduce understeer and steer needed.
- Rotation is a bit more difficult: since rear tyres need a slip angle to generate lateral foce, in corner whole car is rotated in relation to the direction of movement. The more of this "slip" we have the less understeery balance of the car is. This is why good car "hooks" into the corner not needing much steering and understeery one just plows straight needing a lot of steering to turn. Also it means we need a little less steering mid corner than on entry.
For example: cars like lotus 2-11 or Audi quattro need A LOT of steering input on throttle since their balance during acceleration is far into understeer, while more powerful BMW's need little to no steering to corner.
• Now After we know that every corner will need different steering angle, we can start fishing for one that gives us the most front grip. Real and sim drivers do it by slightly moving the steering left and right around the best slip angle to get a feeling for grip. For well balanced racecars the car will respond with visible yaw to small steering input without moving off the racing line. This is because rear tyres are on the limit so a small deflection right or left does not change the lateral force by much. But for street cars that are understeery it's much more difficult as the car won't yaw visibly.
Visual cues are the bread and butter of simracing, it's important too keep car's yaw in mind during practice to develop a sense for grip.
Newbie drivers without experience in visual cues are left with more direct inputs like sound and FFB to help, but remember that they are limited and should not be depended on too much. I think in the beginning it's best to just experiment and find general angles that work for given position in the corner (entry/mid/exit), then keep building up the visual sensitivity.
Here are 4 ways that can help finding optimal steering for maximum grip that can help with practice:
- FFB, as stereo above mentions, usually best grip is made right after peak force, but not too much, some cheaper wheels struggle with generating enough difference so turning on "understeer effect" in options might be a good idea, where FFB drops hard after going past max grip steering angle.
- Reduce the understeer, either by setup, brakes or aggressive throttle use. It's easier to get a feeling for the car that way. Use the information from first part (above) to anticipate what kind of steering you should need so that you won't wonder blindly.
- Sound: in AC by default tyres start to squeal pretty early. So when turning too much, the noise is too loud already and it's hard to determine how much over the edge are you. By increasing "tyre skid volume onset" you delay the moment tyres start to squeal. At 200% they will start to squeal when tyres are reaching max grip. Personally i'd recommend a setting of around150%.
- Skidpad tests, don't leave it at "to do", download a circular map and drive. Stabilize the car in circle and slowly increase speed. Watch for tyre pressures thou, don't turn for too long or the car will start to understeer from overheat. Watch out for too low initial pressures** too as they can mask wrong (too big) steering angles by giving you grip that was lost from wrong setup.
Do test off throttle and full throttle steering too. It's much easier to do when you don't have to worry about apexes.
Lastly there are apps that visualize front grip and (IMHO) provide a nice substitution for g-forces that way.
(**) - It is generally advisable to focus on pressures not temperatures in AC especially when tyres are under-heated,
ps: ayy that was a wall of text and a half, sorry if you found it too much... I'm curious what kind of a response this kind of "guide" will get 
It was great practice for writing english that got out of hand... hahaha
edit: Stylistic corrections, I'm so bad at noticing such errors...
