start with selection of seeds, only use the biggest ... throw away the smaller ones 50:50
Should be noted that this is, if working, only useful when breeding towards higher yielding.
Nevil himself said early on in this thread that some of the best bud came from the smallest seeds and that he did focus a while on seed size but found it inconclusive and strain dependent.
Meaning for some strains (I believe he mentioned the NL) it (seed size) had some meaning, especially regarding yield.
But in other lines (Haze) it was actually the other way around or simply had no meaning.
From my personal, very limited, experience, seed size does not seem to hold a lot of meaning or is at least inconclusive.
I did however notice that the Karma White OG seeds I purchased full price were much larger than the freebies I got. The freebies looked like Sativa seeds and the original package ones like indica beans.
Popped 5 of those, I believe 2 big seeds and 3 small.
Only 3 germed, 2 of the big seeds look good and strong, the 1 from small lookes gimpy and shitty.
Think that is just different seed drops and shitty freebies form the tude though.
What I am trying to say is:
I believe trying to take information out of seeds is iffy business and inconclusive at best.
Obviously better than ignoring seeds as an information source altogether of course but I would be careful about how much you base your decisions on seed shape, size, color, etc.