There are 30 bulls you need to ride on in the game for this achievement. You need to successfully stay on the bull for the full 8 second to get credit for riding on it. Also as bulls only unlock in Arcade mode after successfully riding them in Campaign mode it means you want to get this done during your initial playthrough to save time mopping up afterwards.
To help out I am bolding the bulls below the first time they appear in Campaign mode. They are ordered from left to right in the round order they appear in each stage. So for example the first time you experience the Bruiser bull is on round 3 of Stage 15. Once you've successfully set a score for a bull I wouldn't bother trying on it again later on in a later stage as it will be quicker to just wreck yourself off to save on Campaign completion time.
Stage 1 - Dream Catcher, Deep Water, Panic Attack, Nailed
Stage 2 - Speed Demon, High Razor, Panic Attack, Red Bandana
Stage 3 - Burn it Down, Biker Bob, Heartbreak Kid, Cooper Tires
Stage 4 - Dream Catcher, High Razor, After Midnight, Hustlin Kitty
Stage 5 - Red Bandana, Cut The Cord, After Midnight, Nailed
Stage 6 - Burn it Down, Mystikal, Heartbreak Kid, High Razor,
Stage 7 - Biker Bob, Honey Hush, Filthy Animal, Deep Water
Stage 8 - Cooper Tires, Mystikal, Magic Train, Burn It Down,
Stage 9 - Hustlin Kitty, Honey Hush, Shownuff, Speed Demon.
Stage 10 - Cut The Cord, Fire & Smoke, Filthy Animal, Cooper Tires
Stage 11 - Stone Sober, Hurricane Hustler, Shownuff, Hustlin Kitty,
Stage 12 - Mystikal, Gambini, Smooth Operator, Cut The Cord,
Stage 13 - Honey Hush, More Big Bucks, Magic Train, Stone Sober,
Stage 14 - Fire & Smoke, Mudshark, Smooth Over, Mystikal
Stage 15 - Hurricane Hustler, Fire & Smoke, Bruiser, Hustlin Kitty
Stage 16 - Hurricane Hustler, Panic Attack, Smooth Operator, Honey Hush,
Stage 17 - Mystikal, Honey Hush, Smooth Over, Hurricane Hustler,
Stage 18 - Gambii, After Midnight, Bruiser, Fire & Smoke,
Stage 19 - More Big Bucks, Mudshark, Pearl Harbor, Fire & Smoke,
Stage 20 - More Big Bucks, Heartbreak Kid, Spotted Demon, Hurricane Hustler
Stage 21 - Mudshark, Filthy Animal, Smooth over, Gambini
Stage 22 - Panic Attack, Shownuff, Smooth Operator, More Big Bucks,
Stage 23 - After Midnight , Magic Train, Bruiser, Mudshark,
Stage 24 - Heartbreak Kid, Smooth Operator, Pearl Harbor, Panic Attack
Stage 25 - Filthy Animal, Smooth Over, Bruiser, After Midnight
Stage 26 - Shownuff, Smooth Over, Bruiser, Pearl Harbor
Stage 27 - Magic Train, Nailed, Bruiser, Smooth Over, Spotted Demon, Smooth Operator
If you do wreck yourself by accident on a bull you’ve yet to set a score on then you could restart the stage or what I’d suggest doing is carrying on and take a look at the list to see if that bull appears again on a future stage.
Also although there isn't achievement tracking for this achievement you can go to your stats and see what score you received when riding on that bull. For the achievement to unlock you need to make sure there is a score beside all 30 bulls. If there is a blank next to the bull then simple replay one of the above stages it features in and be sure to not wreck when riding on it.