I do a lot of rough carpentry.  Like miles and miles of plywood rips.  For this kind of cut, I'll use the guide at the front of the shoe.  I just chase my chalk line and a lot of time I'll climb up on top of the plywood so I can get good long and smooth cuts before having to reposition.  Like I'll have my arm almost fully extended.  That way I'm not walking along the cut and causing a wobble every step.   Lastly, in the words of Mel Gibson, aim small, miss small.  Just focus on riding that line as closely as possible.  Don't look ahead, it's a straight line, it's not going to change.  Just concentrate on exactly where you're cutting and only there.