"Designing a List For Word Squares" in the August 1996 Word Ways shows that a word list intended for finding squares can be improved by balancing letter frequencies. In general, we want the fraction at which that letter exists in the word-stock. In particular, we want to enhance the fraction of words beginning with e,i,n or o (and to a limited extent beginning with a or u), and the fraction of words ending with a,i,o or u.
"Bottom-Up Finds Some Squares Faster,"
Word Ways: Vol. 29
, Article 3.
Available at: http://digitalcommons.butler.edu/wordways/vol29/iss4/3