Problem with classes is that you are being exposed to "opinions". They're OK as long as you don't feel you have to agree with the teacher or the workshop participants.
Stephen Sondheim says to get a legal size pad of yellow lined paper and sit down and write, write, write until you get it right and Ira Gershwin says that lyrics are like mosaics. Take disparate lines and string 'em together.
As to content, it's your call.
It doesn't hurt to know about the technical sides of poetry such as stuff like alliteration, identities and rhymes, metonomy, specificity, scansion, pentameters, and all that junk which you can learn from basic books on poetry and lyrics.
But if you don't, and you write good songs anyways, who cares.