There are 60 Events in the Racer Career to get Gold on. This will take about 15 hours and some retrying of events to place first. There will be a few Time Trials that will give you some trouble, but if you keep practicing, you will persevere.
Some tips are:
Learn when to boost. Going up hills and long straight aways will be perfect times to use your precious nitrous.
Explore the shortcuts. Some shortcuts will help you a whole lot and others will mess you up even more. If you are having trouble with an event, find out which route benefits you the best.
Drift. This is one of the better ways to get your nitrous refilled and will help you from hitting walls on those sharp turns.
Do not waste power ups. These will help you during races and hot pursuits. Start the races trying to use brute forces to take out your opponents. When you are getting low on time or almost have a cop knocked out, use your equipment and take them out.
You can restart the event if you mess up too badly and think you are going to lose. On the downside, you do not get any bounty if you do this. So if you are getting 2nd or 3rd place, the bounty you do earn can help you rank up for the rank achievements.