here's my "starter guide"
always do your testing on the highest number tire set that is appropriate for the weather (ie set slicks 1.5 in dry if you have 5 sets, intermediates 1.3 in drizzle if you have 3 sets, etc). Start the race on set X.1 (X being whatever corresponds to the start weather). This is the way I do it, you can deviate from it, but I haven't ever had it select the worn set of tires this way in a changing conditions race so YMMV if you vary from my method here
the engineer's notes screen will give you a general idea of where to start the setup, so read them and get your initial setup done based off of what he says. I use 76 for "high/stiff", 50 for "medium", and 24 for "soft", but you can use what works best for you, I used to use 20 & 80 for the non-medium stuff that that worked ok too.
If your teammate has already tested, then base your setup off of his. If they give you a range of say 32-100, I recommend starting at the lower end of that range since he started that low based of the engineer's notes. Coming back after testing with a range of 32-80 isn't helpful, but coming back with a range of say 32-40 or narrower is helpful. At any rate, the end point(s) of the range are *not* correct settings, though they may be just 1 point off... so if he posts a range of 32-36 for a certain setting, the correct setting is either 33, 34, or 35. I'd test right in the middle at 34 since it will either be right, or rule the other stuff out to a 1 point range which is just as good as being "spot-on".
so now you've got the testing tire set selected and your initial setup based of the engineer's notes -or- your teammate's testing done. Hit the button to do a run and it usually will give you feedback for a few settings. I prefer to move in 8 point increments or half of the range, whichever makes sense. There is a whole article in the "help" section that explains why 8s get you "spot-on" faster than factor of 10 or other numbers. Wash-rinse repeat as you narrow down the ranges and get the settings dialed in.
I can break down qualifying & race settings further, but I'll leave you with the testing primer and this piece of advice - 50 is a low setting usually, and 90 or more is starting to push your luck depending on the exact setting, but that'll get you started. Some of the "pit stop" and "mechanical sympathy" settings will want to be much lower than 90 though
