This achievement requires you to get all 232 stars in career mode, this is the equivalent of 58 different races/mini games. There are 4 stars per race, but you may be wondering, "I can only get 3 stars per race, how are there 4?" Before you start even going for this achievement, I recommend unlocking expert mode by beating all 10 of the Grand Prix's at least once. I also recommend beating all of them on expert before going for this because you will be somewhat experienced in expert mode before tackling career mode.
Now as far as characters go, I mostly only used Sonic with the Handling/Acceleration mods. Boost for the boost races, but really, it depends on the level because some have more turns and what-not. I also used MeeMee and Aiai for ones I was having trouble with, but 95% was done with sonic.
Regular Races: These are standard 10 player races, you must simply come in first. Make sure you get the boost at the beginning of the race. To do this, when the countdown starts, before the screen turns black hold down RT and then release. If it changes color you know you are doing it right, this is vital to success as all the racers in the last area get the full boost on expert.
Versus: You must race opponents one on one until you eliminate all of the rivals. To eliminate one, you must get a significant distance on your opponent or be in the lead when the timer runs out. My tips for this is to try to get a weapon and hit your opponent, then when you get another one, save it for when you win that race so you have it for the next one. Again not too bad, the only ones that took me a lot of tries were towards the end where there are 5 opponents.
Boost Challenge: You must keep your vehicle boosted and prevent the timer from running out. So these can be pretty tricky, but again, nothing that can't be done with practice. I would try to use the acceleration mod for some of these, because you need to drift the corners perfectly or it will ruin your run. You also get one boost power up each lap of the race, use your best judgement on when to use them because they can make or break a run.
Traffic Attack: I again recommend the acceleration or handling mods for this. You must go through waves of cars. For the most part, the cars are scripted, so if you find something that works, it will work most of the time. It's mostly just trial and error. It's also in your best interest to go for as many of the time checkpoints as you can.
Ring Race: These are the drift challenges for planes. You must fly through rings and you can't miss any or you lose 3 seconds, which pretty much fails you the run. Most of them I only had 1 second left. You need to become a master plane drifter for this because of the boost you get and the way some of the rings are. Again nothing to hard here again, but they can be frustrating when you're right at the end and the time runs out :(.
Battle Race: It's an elimination race, you and your opponents have 3 bars of health, and you lose one if you get hit with a weapon or fall of the course. I would stay behind on purpose, because the AI don't fire backwards too much and it is MUCH easier to shoot in-front of you than behind you.
Sprint: You must beat a course best. These aren't as fast as the expert ghost challenges, but still are a little annoying. Here is my advice, use either the acceleration or handling mods, and one the first lap don't use your boost or anything. Before you cross the line for a new lap, use your boost. You will have a little bit of a start on the ghost and you will still have your boost for that lap.
Drifting Challenges: So these were the hardest for me. You must follow the checkpoints and drift on the arrows to gain time. You must make it through all the checkpoints before the time runs out. You won't get the time if you don't go through the purple checkpoint. I used Sonic's handling mod for these. You just have to get good enough at drifting. I will post videos of people doing the ones I had the most trouble with to get an idea on how to do it. All video credit goes to their owners.
Hopefully some of these tips helped you. This honestly is that bad of an achievement, and is easily doable with practice.