Hmm... encores are tricky

If you have a standard setlist what you want to do is balance your events and songs to build in rating through to the end. It's based upon audience 'mood'; you can see these by watching live.
A bit about events first though; you do events not only to help build your crowd but because they are important for your weekly experience points. So if you do two show events in a few shows per week you should be able to get your 3 experience which is huge obviously. So that's why it's good to learn show event stuff.
Keeping that in mind, we do 14 songs in our current set... and we've got songs that get 2 stars, we play those early, they are lower quality overall and then those I know we can add those events we're doing mainly with view to getting our XP but may only get a star or two when done. Then the songs the I know we can count on for 3 stars are saved for our last few songs where we can bookend them with events that get three stars. That builds crowd levels.
Then we leave stage (and you only have to leave stage once btw) and you can only perform your first encore if it says you've left stage but "the crowd is still chanting for more". Then you need to be able to play a song that is worthy of an encore, so it should be your best song at first. Best rating and also highest popularity. Otherwise the crowd can decide they've heard enough and bail.
If they do stick around for your successful encore and they still are chanting for more then, if you have a song that stands out as even better than that one you can play that and they'll then probably head home.
All of this is relative to your songs, your fans, and your usual level. So when we did our first tour we didn't try any but a few failed encores. Then on our second tour we had a song or two that we knew were levels above the rest of our show and started doing those as an encore.
Keep in mind too (and you now begin to see why I always say that there's a lot of things that go into all popo ratings) that your crowd won't respond as well when you are in a new town as one you have more fame built up in. You won't do as well in a lower rated club or if your health/mood is low etc etc.
But, if you know where your crowd usually is at a certain point and you see them a few lower lower then you can decide if you want to pull your songs back from encores to regular songs. I judge it by events that I use as my 'anchors'. Songs might change/shuffle due to popularity and jam level... but the events are my signposts.
EDIT:
Here's a link to our recent Paris show, that we broke through for a 'good' rating so you can see what I mean about the events and songs building to the end:
TDG Paris
So if Palmer spits on the audience (which always gets 3 stars lol) and the audience isn't at at least 'pleasant' I know we're lower than usual and may have a hard time getting our 2nd encore to go.
In this show you'll see they were going crazy even after our 2nd encore which is new for us

but we don't have a third song to 'top' or meet the four stars our other encores got so there was no reason to add another song that would only hurt our rating so we just let them just go home happy.
Also, April only got three stars for her striptese after getting 5 stars in sex appeal, 5 stars in basic dance AND after I got to 3 stars in Erotic Dance.
