Front and rear wing angle setting -> downforce balance (higher angle: higher downforce), speed balance (lower angle: more top speed, medium effect) and handling balance (higher angle: more oversteer, small effect)
Suspension stiffness setting -> handling balance (softer: less understeer) and speed balance (softer: less top speed, small effect)
Gear ratio setting -> speed balance (shorter: more acceleration) and handling balance (shorter: more oversteer, small effect)
Tyre camber setting -> handling and speed balance (increase negative: less understeer and less top speed, medium effect)
Tyre pressure setting -> handling and speed balance (increase: less understeer and less top speed, small effect)

Any given track/car combination has an optimal downforce, handling and speed balance. It doesn't matter how you achieve it using the different settings. Wing angle setting is the most important setting as it influences all 3 balances and is not influenced by another.

I always keep both front and rear wings the same angle and get a good setup. In real life increasing front or rear wing angle would either lower understeer or oversteer. In the game the effect of both wings on the downforce balance is the same.

First thing tot do is get a reference setting. I keep track of all previous settings in a notepad. Remember that your car changes and so do your settings. If you don't have a previous setting, then look to the track characteristics. Low speed corners require higher wing settings and more acceleration. High speed corners and straights require less wing angle and more top speed. Use a (slightly) different setup for both drivers.

Ok, now send your drivers out for some installation laps. Start a 1 lap stint in race trim (most important trim imo). Bring your drivers in immediately after releasing them for first setup feedback. You don't need feedback while on track. Combine feedback from both drivers to adjust the settings in the right direction. Usually adjust one click of ratio/stiffness or 3 degrees angle at a time, more when it's way off. Make sure you get a different placing on each balance (except when excellent). Adjusting in the wrong direction isn't a bad thing in this phase. Send your drivers out on a second same (race trim) installation lap. Once back in the pits, you can compare feedback from the 2 laps per driver. With 2 reference points on each balance you can theoreticaly pinpoint where 'excellent' should be (ok-good-great-excellent-great-good-ok). Remember excellent can lie 'after' two close greats, but it can also be in between. Tyre camber and tyre pressure is for fine-tuning, using these makes both handling and speed balance move in opposite directions. If you need a medium adjustment for both handling and speed for exemple to the right, first move either one to the right using 1 click ratio/stiffness, overshooting the optimum. Now use camber or pressure to make both balances move to the desired position. Mastering this trick takes some practice off course.

You can now send your drivers out for the longest possible race trim stint, still on the same tires. On track feedback should tell tell you if you've done a good job. Don't abort the stint when given negative feedback. You can correct this afterwards, now with 3 reference points on each balance. You should now have a 98% setup on average and still have time in practice you can use for maximizing setup and knowledge both.

In the setup section we started practice on race trim. These stints should be on the softest tyre, which you're gonna use in qualifying and, most of the time, in the race. After the first long run sometimes you've already got max knowledge (level 3) on your trim and tyre. If not, send out one driver on another max laps racetrim and the other on max laps qualifyingtrim. Bring in your remaining racetrimdriver(s) after knowledge reached max and start a qualy stint. On most tracks you can get all knowledge on race trim, qualy trim and your favorite tyre.

Use max 2 sets of tyres per driver in free practice so you got enough of them in qualy (2) and race (3).