a lot of it is hitting houses that are on the other side of the road. Easy% runs on a set path and uses restricted cam and boundaries so you gotta learn how to move around with these boundaries and sometimes the levels loop around the same road, so you can hit houses that are on the other side of the road even if they're out of view.
forgot to mention that you can also do double speed boosts by boosting on a sidewalk then going off the side, and doing another boost. Recently. i also discovered you can gain a lot of speed by canceling your boosts by braking with B then boosting with A a little after, so you keep hitting A then B then A and so on so you continuously keep boosting. This prob wont help much with Easy % Runs but def helps Medium %