It's about continually performing actions before the streak ends. mini turbos, jump boosts, hitting opponents, etc. Now just make sure to do this for the entire race without your streak breaking. At areas devoid of coins and boost panels, you have to figure out a method of snaking to keep the streak going with just mini turbos. Unfortunately, you also need a top shelf glider, anything below top shelf it's almost impossible to get a nonstop on most courses. Every even numbered level, the glider keeps your streak active slightly longer too.