Move somewhere warm so you can autocross every month of the year.
Find a region with longer than 25 second courses and more than 4 runs. Not a lot of seat time there!
Ride with someone else if they will let you to get over the "sea of pylon" syndrome and get the "sight picture"/typical speeds they are seeing. This will give you an idea of how violently (but smoothly) and late (but not too late) you need to brake, and the subsequent transition to cornering/acceleration and then to progressively harder acceleration out of the corner. All inputs are smooth. No suspension jerkiness allowed. Notice how good autocrossers will turn everything they can into a straight or at-least as much acceleration as possible.
Practice hitting your apexes on the street at moderate speed, OK faster than moderate, but safe for conditions. Practice late apexes. Practice late braking and trail-braking before that 90 degree left hander. As you get better, practice left-foot braking into that same corner, staying on the gas as you ease out of the brakes. Learn to modulate your left-foot braking at normal speeds before attempting it at an autocross.
Experience what happens when you let off the throttle suddenly in the midst of that fast corner at high RPM. Once you learn what a spin feels like, you will remember not to let off the throttle unless you get right back on it after kicking the rear around. Experience what happens when you give it too much gas in a slow corner...that grinding understeer. Your slow time and high tire bill will convince you that does not work.
Find a curvy, isolated road and practice at reasonable speeds, staying within the speed limit and YOUR limits! Of course three years of driving in Germany could not hurt!
