Tire pressure and downforce
I just run round the nurburgring with telematary on then try and get 32psi out of the tires from lap 2 -5 and then also try and get the temps as balanced as possible across the tire under braking and acceleration if your camber is high you will always get a little peak on the inside but it should settle down in the straights . As long as your getting the best footprint on the road from the tire it should be all good . Especially under braking and accel then your stoping distance and accel should be spot on. If I was good at maths I would use a theory but I like to do it the dirty way on track and feel it as you tune and move things about till you know you can’t get any more out of the car then I am happy 
. Usually takes me about 10-15 laps on nurburgring to tune a car properly then it should be good on most tracks !
Also I forgot to mention about downforce . Yes you will get a peak from time to time on the inside of the tyre wall which is fine as this proves we have camber to carry us through the corner with the best footprint , like I said "I tune 90% for the nurburgring " so high downforce in most higher classes is needed thus giving you more pull down on the car and increasing the footprint on the track , which also has to be countered with tire pressure too, as the more downforce and pull down on the car the more the tire will sag out at the sides because of the pull down of the car from downforce this also has to be countered with tire pressure to compensate as the rims will bang out into the track as you hit bumps and dips and jumps . Most people don’t realise this so they increase bump stiffness or springs thinking they are bottoming out but this is not case if you see on telematary when running on the ring that the sprigs are going red at compression points this means you are bottoming out and need higher bump / stiffness or ride height to compensate , but if they stay green but you hear banging and the car joults about this means the rims are hitting the track through the tires as the pressures are to low so need to be higher due to rim ground out this is compensated through pressure adjust .
Like i said not many know this so a good tip for the comunity for free
It’s will help with the general car demeanour round the ring and bumpy tracks and make it more stable if you get the balances right .
Camber , toe and caster
Camber is used to give the car a greater tire footprint in the corners so higher camber at the front then the rear is also advised as your front wheels do all the turning with steering and camber is great at giving you stability in the corners , lower in the rear as this is mostly where your drive comes from so a higher footprint will give you stability and power transition onto track.
Don’t be afraid to give the camber high settings either some tunes I have go really high .
Toe is something you should only play with when you get to advanced tuning as this can be used to get the twitchiness out of the car and also can be used to give the car higher mechanical turn in by front and rear at opposites or the same to give stability but again use this only when you really need to because this can make the car really unstable if done wrong . Most fast tunes will use a rear adjust on toe .
Caster can be used to get the car to turn in more and less depending on the car and stability. Your camber will also increase with caster so I always try and get this as low as possible until the car gets out of control and turns in loads then back it off just enough to get the best turn in possible but keep stability .
Springs settings .
This is completely dependent on what the car is , weight distribution , drivetrain and car feel . So a front engined rear wheel drive would need higher springs at the front and lower at the rear but a mid engined rear wheel drive would need higher springs at the back and lower at the front . A front wheel drive front engined car would need higher front and lower back . Then you get 4wd but the same principles apply but less of a difference between the both . So what I am saying is it is very dependent on where the weights and power is and goes too . The hardness is very dependent on driver preference although I use a mid to hard setup on most cars .
Rebound and bump
This again will work on the same principles above with how far the sliders are apart from each other but there will be a huge difference on the rebound which will be mid to high on sliders to get stiffness without making the car feel soggy and slow to respond . The bump would be low but the same differences apart as the rebound , although in some cars and tunes people have used a very low rear bump in RWD cars to soften the slide and make the back end sit as much on the road as possible with as much traction on track at all times .
Differential
This is the last thing I normally play with to finalise the tune . It’s a great tool to get the car to turn in / out and keep the back end tight or loose . So low acell will give you less spin before the wheels lock together so lower this is your sliding out when you hit the throttle in the corner not to much as you will not get any pull or push out of the corner and miss the apex . When you get a sweet spot you will get pull from the rear nicely without it spinning round to much . Decell is almost the same principle but reversed so when you swing into a corner and the back end slides out before you hit power then higher this until you get a very small limited amount of slide as you need a little to help with cornering but not to much so when balanced between them both you can get your back end to help you through the corner in both decell and acell it’s also personal preference and how you drive as tuning for the general public is trying to get the best but tuning for yourself then you can get it how you drive . When I tune for hot lapper’s then it has to be different for each one as they all like this slightly different so finding what you like is important.
4WD is the same just on the rear diff as above but the front diff you need enough accel to pull you out of a corner with out loading tracking in the front wheels or you will loose traction and steering and fall out of the corner and overrun . The decell at the front I always leave on 0% so you get no drag on no power or again it will pull you out of the corner . The split in power will depend on weight and power distribution (in an Audi it’s about 40/60 to the rear and on a skyline about 30/70 to the rear )
FWD
That’s the same as the front part of the 4wd setup above.
AERO
This can be used to give the car a balance on cornering and straight line speed in higher classes it’s always full with maybe a little lower on the front and in the lower classes it needs to be set to how the car feels and track specific to get the best balance and best hold on the car . So high front will give you better braking and steering in corners and higher back with give you more traction in the corner and improved stability under braking but this all comes at a cost in staight line speed and acceleration so a balance is critical on this .
Gearing
This should be normally a stock gearbox unless in track specific tuning and trying to get your final gear to be just under the redline in the longest straight on the track your tuning on is always a good general place to be , although in some cars I may tune for a 5 speed box even if it has 6 gears so you lose less in gear changing . There is also the final drive this should be changed depending on where the power is in the car with torque and BHP so higher for a high revving BHP lead engine and lower for a high torquey lower BHP engine.
Again these are only my own preferences and how I tune , everyone will have slightly different opinions on tuning so get what you can from as many people as possible to help you find your own path in tuning .