1 So happy peace they made and fair accord: 2 Eftsoons this liege man began to wax more bold,
Eftsoons > Soon liege man > {Vassal; faithful follower or subject} wax > grow
3 And, when he felt the folly of his lord, 4 In his own kind he gan himself unfold:
kind > nature (or perhaps this is a misprint for "mind") gan > did unfold > reveal, disclose; make plain
5 For he was wily witted, and grown old 6 In cunning sleights and practic knavery.
practic > artful, cunning
7 From that day forth he cast to uphold
cast > decided
8 His idle humour with fine flattery,
His > [Braggadocchio's] idle > empty; vain, trifling humour > frame of mind