Brush movement on Okami, Wii version

Solution 1:

What you're probably doing is pointing somewhere, holding down the A button, and then moving your Wii remote. I've found that by doing this, the pressure on the button makes your hand move and your aim slightly off, causing a slight "curl" at the beginning of what should be a straight line. The game tries to figure out what you're trying to paint, but the change in direction at the start usually makes it too unlike a straight line to be recognized as such.

A better technique is to start moving the remote first, and then hold the A button to make a straight paintstroke.

Solution 2:

If I recall, the Z button on the nunchuck will force a straight line, which will help a lot for the Power Slash segments.

Some of the Wii motions can be rather difficult to pull off consistently, and the most troublesome techniques can vary from person to person. Until a late game brush technique I personally had far less trouble than others I knew playing the game.