3 star ranking is incredibly rare. You must come 1st in all races and lead by a considerable ammount (e.g. dont take over just before the finish line) and finally you muct do tricks on pretty much every jump, even the obscure ones you may not realise even exist. I only hav one 3 star and im a mario kart vet. 2 stars is a much easier and is usually obtained by cominf 1st in all but maybe 1 race were you come 2nd or 3rd, and you must do tricks on most jumps. 1 star is abtained by coming 1st in all but 1 race where u may come 3rd or 4th or 5th. Depending on your placing you should aim to trick most jumps. This is not fact but based on my own experiences and i believe there is a very complex calculation to figure it out involving time spent in the lead, how many items you are hit by and defend against ratio, overall placing, placing in each race, number of tricks, use of skidding etc....in the manual is simply states you will be graded on you racing skill. Hope this helps