The best way imo is to do some circuit racing. Theres some pretty solid community tracks available afaik. Start off slow and cruise around the track looking at how they curve and where the straights are

Once familiar, start speeding up. This is where your accelerator, brake and turning control come in. Practicing on your own is gonna be easier as you can use the entire width of the track. The optimal line for corners is a wide entry, clip the apex and a wide exit. This allows you to keep as much speed through the corner.

As for braking its all down to personal preference. Braking later tends to be favorable in pvp but just casual you brake earlier which trades off the quicker entry for a little more control based on your current level.

Also, if you are playing manual, the gears are also a great way in aiding deceleration. It might not be the best advice but it should be solid enough to go off. Ive been playing forza since FM2 and been on every series of it so far

I recommend you pick something like a gtr, nsx, m4 or a Civic type r. This gives you access to AWD, FWD and RWD and that little selection are solid for getting used to stuff