for me gridding guitars is a no go! if you grid your guitar it has no feel left and to be honest gridded guitars sound much like midi programmings. try to listen carefully what sounds off and make a correction only on this parts. be aware when you make the correction and you wanna put a note to a beat transient or a grid line you have to put the loudest part of the note on the grid not the beginning! (a normal guitar strokes starts with some pick noise and a buildup to the transient and the real transient should be on the grid)
mostly its just practice practice practice! there is no short cut... just record all the time and correct your recordings until you can do it by heart!