practice is the answer to be sure,
I didn't like mine at first..then I got better with it..I like to scribe a center grove and then mark the spot, and freehand it, no guide.. Seemed to work best for me..my main issue is the start ...get yourself positioned with the slot surface pointing up...I brace myself so I won't be wobbling. Then I turn the tool on and let it just barely kiss the area to be slotted, once you get an initial cut going it seems to track down well. I have always had a fairly good eye for free handing things so possibly you might prefer a guide of some sort...