There are 4 variables that can be manipulated for each hand and foot hold on a boulder. How you alter these variables will ultimately dictate the style and difficulty of the boulder. 

• Severity: Using better or worse holds. Size is not the appropriate term.
• Distance: The space between holds in a single move.
• Orientation: The position, spin, angle, etc. of holds.
• Direction: The direction of travel between holds in a single move.

Consider these variables when bumping up against creative roadblocks when building boulders. More practice considering these will lead to increased skill in manipulating them.