After thinking about motifs for a little while, it’s possible to get carried away by them. So what amount of repetition and variation is going to work for your text, what’s too subtle, what’s heavy handed? Of course there’s going to be a wide range of effective possibilities. I did a quick bit of math and figured out that “blood” appears, on average, once approximately every 815 words in Macbeth, “green” appears once every 2,479 words in The Great Gatsby, and “cannibal” appears once every 6,337 words in Moby-Dick, whereas the more obvious motif of whiteness shows up about ten times that often in Moby-Dick). The word “blood” is, of course not the only way Shakespeare evokes the murder or it’s leavings — there are a few instances of “bleed,” “red,” “spot” and the like as well. Similarly, the whole green thing in Gatsby is part of a larger theme that encompasses a range of colors (the yellow car, flashes of red, the varying colors of leaves throughout the seasons…) Although these metrics are a little fuzzy, it seems safe to say that a very heavily hit motif in these three works (blood and whiteness) comes up on average every few pages (although many of the occurrences are in fact clustered together in certain scenes). A slightly more obscure motif like the cannibalism in Moby-Dick comes up much less often — in this case less than once every twenty pages — but nonetheless often enough that it is noticeable and indisputably an idea the author wants the reader to ruminate on.
So, with these thoughts in mind, take an inventory of some of your motifs and the number of instances that that occur as well as the pattern and frequency. Use your awareness to cull, augment, or vary as you think will best advance your story.