wHAT'RE some tips to successfully land Vi's Q when ganking?
No easy way for that, I am afraid.
Know what your opponent is capable of. Try to predict their movements, but if they are not that good, you are just going to outplay yourself. If their movement is unpredictable, you can consider going in with R instead (if it is a guaranteed gank) and use Q to get them once they try to escape.
Skilled players are rarely going to get hit by Vi's Q, unless your teammate makes use of his skillshots as well, which should be the whole point of ganking, after all