I understand that you don't want to "ruin the fairy tale" at the beginning, but if you don't tell people, then you're stuck taking it or telling them a while after the fact... making them feel like they entered the relationship under false pretenses.
Think about it. They start a relationship with someone who seemingly likes the same things they do. Then once the relationship is established and it's not so easy to just say "we're not compatible, let's stay friends", you tell them that actually, this and this are things you don't like. I think if I were them I would be annoyed that you were dishonest with me and let me get attached, without giving me a real choice from the get go (my annoying - to you - habits, or a relationship with you) and therefore it would feel like you're twisting my hand.
It would especially annoy me if the things are small things that I don't mind changing. Because then, it would feel similar (to me) to when poly people cheat: there wasn't even a point in using deceit, yet you did anyways (I realise you're not trying to deceive people. I'm trying to express the way it would feel).
If the things are small things, I wouldn't have cared about changing them from the start, and I would have appreciated your telling me from the start. If you told me later on, even though there are things I wouldn't have minded about, I would be much more upset about the whole thing, because I would feel like you tried to trick me for no good reason.
Not to mention, the relationship up till then might seem like a lie. What did you actually like? What did you hate but not tell me?
No, there are way too many issues with bringing it up later on. You need to say so from the start. And expect your partners to let you know, too. You don't have to make it about them. When you're at the "learning about each other" stage, talk about yourself. "I don't like PDA, but I like kisses in private" or "I care a lot about tidiness, clothes on the floor drive me crazy" or whatever it is. Don't limit it to things you know they do, either, just let them know everything you can thing of about you. This way, they can decide to date the real you, not an image you're projecting.
And encourage them to do the same. It will help both of you know how compatible you are, and if you'd be willing to compromise on the things where you are not compatible.