In the line before this, Wordsworth mentions the bird singing a "love-prompted strain". He is probably referring to love that the skylark has for its nest and babies, since he refers to that in the first stanza. "Twixt thee and thine a never failing bond" refers to that song the skylark sings to her nestlings (twixt=between, thee and thine=you and your family) and it being a bond that never fails between them. The nestlings can always hear their mother's song, and it is a way for the mother to let them know that she hasn't left them. He goes on to say that song also "thrills...the bosom of the plain", meaning, that song also is beautiful to the earth below (the plains). Then he states that it seems that her song, which is a proud privilege to sing, occurs no matter if it is Spring or not ("independent of the leafy spring").
As for literary techniques, besides rhyme and meter, Wordsworth uses personification when he refers to the plain-its bosom thrills at the song. A plain can't have a bosom, or thrill, so he gives it human-like traits there. Then he also uses metaphors when he calls the song a "never-failing bond". I hope that this helps with the interpretation and analysis! Good luck!