how do i ride his face ????

my bf has been asking me for 2 months to ride his face , as another method for oral sex . and i’m afraid something might go wrong ! first off , my legs have a little weight on them , i mean , i’m tiny but my legs are on the big side 😂 and i’m super SHORT so how would i end up on his face ???? and i’m just afraid i might literally sit on his face and hurt him or something like that ! like ive been saying i’d do it , but i just need to learn how first .. and ik he really wants to try new things with our sex life , but i’m just afraid i’ll hurt him !😂🤦🏽‍♀️ please help