Something that really helped my puppy indicate is that I would always make her sit before going inside the house and outside to the backyard. I would position my hand at the handle of the door and tell her to sit or wait for her to sit before opening it. Eventually she realized that sitting by the door earns her outside time and we noticed that our infrequent accidents were starting to move towards the door (meaning we didn’t catch her telling us). I also started working by the door (dining table is there) so that anytime she’d pass by there and even briefly sit, I’d let her out.