For guided tours, I tip based on the quality of the tour. I've had a couple very bad tour experiences and didn't tip at all. We do one tip that covers DH and me, up to 20% of what we spent on the full tour. From what I've observed, people tend to tip a few bucks (regardless of tour cost) to about 10%. I had a snorkel cruise where the guides took us out to see whales and dolphins and then took back us in to snorkel. I tipped them a bit more than 20% because they went above and beyond.
For breakfast, if it's a continental breakfast and I get my own food and clean up after myself, I don't tip. If someone gets me something special or displays really great service, I tip a few dollars.
If someone takes even part of my order, I tip. For instance, if there's a buffet, but you order your eggs or your beverages.
Here's a place I differ from some - if I have to call the desk to fix an error in the room e.g. there's no hairdryer, the remote needs batteries, there's no shampoo in the bathroom (once I had three conditioners and no shampoo,) I don't tip the person who brings whatever is needed to correct the error. Maybe I'm just a grump, but I'm not "rewarding" someone for restoring what should have been there in the first place. However, if someone brings extra towels, extra coffee, extra shampoo, I'll tip.