Q: ok i've got first verse, chorus, second verse, second chorus. now what?
A: take a deep breath, and run through the song. the song already has a strong identity. ask the song what it needs, if anything. to do this right, you need to keep cleaering your head and running the song from the beginning, and right as you are getting to the end of the second chorus, that's when you will have the clearest idea of what needs to happen. Remember to remain open to all possibilities! including nothing. this part of songwriting is something i call "finishing" because there is really no telling what it's going to need. every song is different. i've heard so many songs that in my opinion fail at 'finishing' because they didn't take proper care to figure out what's best for that song. in other words, having a bridge when there shouldn't be a bridge. having the wrong kind of bridge. bridges are unpredictable anyway and this ties in with the 'be open to anything' strategy. this is a very sensitive part of the process, and every song needs something distinctly different, and quite possibly nothing. you will only know clearly after doing a full run through, and start paying attention about halfway through second chorus. many times your next step will be something that almost interrupts the end of the chorus to go to a different thing. other examples of things that work in some songs are: another verse with no lyrics. another chorus with no lyrics. maybe a totally different thing with no lyrics. another chorus with different lyrics. a totally different thing with lyrics. but this is a sensitive issue and every song has very distinctive needs, so you need to make sure you are doing full run throughs and really let the song decide what it needs or doesn't need.