Ah. I guess from the above you're having problems with the Paint Brush.
As well as altering the settings, I recommend not working at too high a zoom level with this - the accuracy I think is measured in pixels, and so the closer you get to the work, the further it can drift out. I'd also suggest working with a decent size brush, nothing below about 4pt ... speaking from experience ;)
Also double-click the brush you're using in the Brushes palette and see what its settings are there, it may need tweaking
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Mon 23 Jan 2012, 0:12,
archived)
Also double-click the brush you're using in the Brushes palette and see what its settings are there, it may need tweaking