Having had over forty years of experience I'm offering some does and don'ts that I think you'll find extremely helpful in this art and it is one that takes a good deal of practice. Once you've found a willing partner and while I've been told no at first I've not had one woman who has refused me. There is something that they find likable about it. Perhaps it is the attention that you pay to their titties. Perhaps it is seeing themselves with cum all over them. I think in a couple of cases for me especially early on in my career it was I don't want to get pregnant. Yes two girls in particular I can remember that they weren't on the pill. I've had some tell me that they have a climax, they get that excited. With the exception of one woman none of them had ever tried it before. The woman that did went into great detail of exactly what happed which made the tittie fucking even better. Never try it on a first date. You can and should suggest that this is something you'd like to try sometime that the thought of spraying their titties with cum is a turn on. Beyond that say nothing. You've planted the seed and got them to thinking. I've had women on the second date suggest to me that they would like to try it reinforcing what I said.
1. Foreplay is a big key to the success of this. I spend a lot of attention to her breasts giving them a nice kneading, licking, sucking, cupping, and biting. A minimum of ten minutes. While I'm doing this I'm talking to her telling her how special her breasts are, how much they turn me on, what a special treat this is for me. While I'm doing this I'm either rubbing my cock against her pussy or I've already have put it inside her. My goal if possible is to make her climax while I hold back and wait. You're going to get some sort of response from her such as is there something wrong? To which you can respond with using her finger in her cleavage, or just whispering into her ear that you'd like to fuck them and cum all over them, that is why I'm holding back. She likely will not object. Once you move up and sit or straddle her stomach you can have oil ready to go on the night stand. Don't use too much! You can lovingly massage enough on her tits to make them more desirable or just squirt a small amount in her cleavage which is all you're really going to need. I've used scented lotion, olive oil, and baby oil. All of them work equally well. If you do use too much they'll be erotic looking but so slippery that your cock won't stay in her cleavage which gives you only one option; a hand job stroking your cock against the nipples and titty flesh until you explode.
2. Smaller breasts are a bit more of a challenge and let's face it most women are in this category but it is still relatively easy to do. Some women with smaller breasts are a bit sensitive of the fact especially if they know you've been with a woman who has bigger titties than she does. Rather than using your entire cock show her how to squeeze them together and wrap her hands around them. You'll be concentrating on massaging the cock head only. You're up and down movement will still allow the head to pop out which is a turn on for many women. They like to see this especially as it becomes harder and more sensitive. At this point comments are in order such as I love fucking your titties, I could never get enough of this; do you like what I'm doing to your titties? Encourage her to talk dirty to you. Remember that she has already had her climax and is somewhat relaxed so she'll be more receptive to the talk. I know that for me when she says I want you to come all over my tits it turns me on even more. You can comment afterwards that you're not too small at all. Just look at all of the cum you generated.
3. While you're sliding up and down your cock is very close to her mouth and you can ask her to suck on it while it is close to her lips, an additional turn on. As this is going on you can ask her if you should cum in her mouth or spray it all over her tits or give her a pearl necklace. I like to spray or hose them as it gives me the opportunity to spread the cum around with my cock especially concentrating on the nipples. This is also the time to say how nice they look with my cum all over them. Women like it when you pay attention to their bodies which will make it much easier for them the next time around. I've also if they agree, giving them a little bit in their mouth, just a taste and then finish cumming on their titties.