If you're riding a fairly easy bull when you are
in the green zone, left click your mouse and the bull will buck, thus
giving you more points. Also press the space bar. This is the same as
clicking the mouse for a good buck.
If you are riding a level 1 or level 2 bull, try and keep your blue target in the yellow area and not in the green. This will possibly give you more points, though I have tested it numerous
times and it tends to only work about 60-70% of the time. Nevertheless, worth a shot.
A method that will help you is 'spurring'. Spurring is when you are riding, you take the heel of your shoe and kick the side of the bull
using your spur (this also gives your more points). To do this in the game,
press the "S" button repeatedly to spur the bull and get more points.
Another hint that only works part time, is using the "B" button. I like
to call this the "extra hard buck." This button also bucks the bull, but
much harder than pressing the space bar or left clicking the mouse.
For me, this hint works most of the time, about 75-80% of the time.