First...The best solution I've found is to shift solidly through the gears.
Second...To do that the shifter lever needs to be in the right place for your foot.
I had mine modified by DH Racing. Had this done last year and I aligned the shifter lever to fit me on the stock seat. Last month I get used Ultimate seat here on the forum, which sat me back further and through my shifter lever out of alignment. I got back under and adjusted it again to solve my occasional "in-between or missed gear" shifting problems.
Probably the best mod so far...OH! Forgot to add the mod shortens the shifter throw at the lever, improving the odds you won't fall "in-between" gears.