Roll direction does not matter.

In classes above basic roll direction will be more important for positioning in the box.

Say you have a spin that requires a 1/14 turn that will take you across the box instead of left or right, your going to want to spin in the direction that will make the next maneuver go the correct way.
Example,
Your flying left to right going into the spin. Your flying a line that is far enough out but, coming back at you for the x-box maneuver will not leave you enough room. That spin needs to rotate left so at the end the x-box line will fly away.
If you got blown too far away entering the spin, you can rotate right and use the x-box segment to bring you back.

In upper classes you will have figures that have more elements to them. Some of those figures will have you roll one way and then snap the other. Again, initial roll or snap direction isnt critical as long as the next part of the maneuver is the other way.
Example,
From inverted, 4 of an 8 point roll with and opposite direction 1 positive snap.

Dont go watch a competition. Go fly in one.
Its a blast and you will be able to get a ton of help while there.