I'll try Daisy. In lyric based music, generally speaking, no fills until the singer or soloist is done "speaking". (Even then might not be a good time either) You have to listen for the appropriate spaces. Not all spaces are appropriate to fill in. Spaces within a solo are fair game, it shows you're listening if you can drop a quick ditty in within a natural space in a solo. That usually works nicely, because you're not stepping on anyone. Music is like conversation. Don't be rude and interrupt. Don't think you have to mark every transition either (verse to bridge, chorus to solo, solo to verse etc.) It builds tension when you don't fill before the start of every solo. Small picture = "oh here comes a transition. A fill would fit there. Here I go. Wee! Big picture = "oh here comes a transition. I'm gonna save my ammo until the peak of the solo, right at the last second before it goes back into the verse. It will have much more impact there" Bam!
Seriously, fills should be necessary. Just because you can fit a fill in, doesn't mean it's necessary. I leave many a transition unfilled. Many. I hear a lot of drummers play things that aren't necessary, but the spot they pick is an "acceptable " place for a drummer to do something. IMO, that usually detracts, and tells me that the drummer doesn't have the big picture in their sights. Drummers typically play fills at the transitions. Fills aren't always the best choice at transitions. More times than not, just keeping the groove going during the transition works so much better. Fills release tension. Not filling builds tension. You have to pick the right spot to release. Just because a transition is approaching, that doesn't mean you have to do something there. You have to weigh if it's better to release, or better to hold off. Hey sometimes it is better to release. It's a musical maturity thing. When in doubt, don't fill, just keep on keepin on.
I try and keep the QNP going during a fill, lest you let it drop out and lose groove. In the blues based music I play, I pride myself in keeping the beat nearly all the time, because in blues, fills detract, unless they are necessary. I do ornament the beats with as much nuance as I can muster, that's where my focus is, and my fills are used only in spaces where it would sound worse not to fill.
When music goes from the one to the four, or from the four to the five, a lot of times, just marking it with a simple crash is better than leaving it alone. I don't consider that a fill though.
I cut loose on endings, but I don't hog anything or go on for another 10 seconds while the guitarist has his neck perched up in the air waiting for me to finish. That's rude. When someone lifts their neck up, I finish up whatever I'm doing, early if necessary, to make sure we look in sync. Very important for the guitarist to not leave them hanging. He/she will appreciate that. Endings....I like to think of them as a musical "dismount". Just like in the Olympics when they leave the balance beam. Gotta stick the landing.
Too many drummers think they are defined by their fills. That's their artistry. Hogwash, Drummers are defined by their beats and feels. Fills are a treat type of thing, not the main course. Drummers justify their overuse of fills by saying that the guitarist has so much freedom and can do almost anything at anytime, why can't I? Two different jobs, you cannot compare them. A drummer must know his role. No one else has the responsibilities a drummer has, and you can't compare playing drums to any other instrument, it's a different discipline.