No such magic forumula exists I'm afraid.
Every DVD is different, I usually take the menu quality down to 40% to improve the film quality. You can also strip out extras before processing with IC7 by using Ifo Edit or DVD Shrink but this can lead to compatibility & playback problems of the final disc.
The other good thing to do is remove unwanted subs & audio and then increase the movie quality with all the space saved.