I draw the darkslide about 1/3 of the way out. Plenty far enough to check the end of the rails to make sure the film is loaded properly -- and reduces the opportunity for dust (and beard hairs!) to fall onto the film before the darkslide is slid back shut.
Our students tend to freak out a little about the idea of loading film holders -- but I just tell them that compared to the loading of 35mm film on metal reels (which they should have "mastered" by this time) loading 4x5 film is a breeze!
When I first started leaning LF (4x5) and of course I still am I had some trouble making sure the sheet of film was in the proper slot. I now only withdraw the slide as far as the start of the rails. Withdrawing it any further accomplishes nothing and makes finding the right point to start sliding the film in rather easy.. at least for me.