I used to roll the bike a bit before I could shift into first (sometimes, rarely) but now when that happens, I maintain steady pressure down on the shifter, clutch in, and slowly let the clutch out. The tranny will go into first before you start rolling forward. In fact, you can then pull the clutch back in if you are not ready to go yet.
After I worked that out for the R65, I tried it on my Triumph with incredibly noisy ineffectual results. But it does work on my car when IT doesn't want to go into gear smoothly. Weird.
I think I got the tip from Duane Ausherman's web site.