Make your intentions clear. If you genuinely care for or respect the lady you met at a party, for example, don't mislead her by claiming to be interested in a long-term relationship when you aren't. Show your faith in her by being honest from the start, and you'll have a better chance of earning her trust in return.
Don't just look at her chest, or any other part of her body she may choose to hide, but also take note of what she is wearing and how this affects you. If she's wearing a shirt with buttons down the front, for example, that might be a signal for her to open up about herself more freely. Let her lead the conversation if it seems right to do so; don't force topics upon her that aren't coming up naturally.
Of course, you shouldn't just follow these tips without thinking through why the woman you want to get to know better trusts or doesn't trust you. There could be anything from you breaking up an existing relationship to help her move on (or even yourself) for a more permanent commitment later. Only you can really know what's behind your partner's actions or decisions, but if you make it obvious where they fall on the spectrum between trust and lack thereof, then you'll be well on your way to getting her to change her mind.
Without regular, open, and honest communication, it is nearly difficult to create trust. Prove yourself to be an active, concerned, and interested listener, and speak to her about your thoughts calmly and frankly, and you will gradually but steadily acquire her trust. Show that you are willing to make decisions together by giving each other responsibility, and let your partner know that you want them to feel comfortable telling you what they think.
The best way to build trust with someone is by being trustworthy. Do whatever it takes to show her that you are committed to their relationship, and that you are not going to change no matter how much she wants you to. Make a decision to do what needs to be done to move forward with her in order to keep the relationship healthy, and let her know that you are ready to work through any issues that may have caused problems in the past.
Show interest in her life outside of the relationship and let her know that you are there when she needs you. Give her time and space, but don't be afraid to reach out if you need something from her. Trust is one of those things that can't really be forced, but it can be encouraged!
6 Ways to Gain a Girl's Trust
If she isn't comfortable, respect her personal space and limits. Tell the girl how you feel about her so she knows you care. If you've spent time together and want to know what she thinks of you, be upfront and honest with her. Tell her what's on your mind and be open and honest with her. Don't try to change who you are for someone else; if she doesn't like you for yourself, then you haven't lost anything by telling her so.
She needs to know that you're not trying to change who you are for her. If you have feelings for her, tell her directly. She may not say yes right away, but keep trying until you find out. Don't just assume things will work out between you two.
Finally, remember that you can't control how she feels about you, only you can do that by showing her that you're a good person who cares about her.
The worst thing you can do to regain a girl's trust is to contact or visit her until she feels absolutely smothered by you. Instead, tell her you'll be taking a step back and waiting for her to reach out when she's ready.
This isn't to say that you should wait years before trying to get back in her good books. Just don't force things. If she wants to move forward with you, she will let you know. Otherwise, you were just wasting your time.
The best way to earn a girl's trust is to show her that you respect her space and allow her to feel safe around you. This doesn't mean that you have to accept any kind of behavior that makes you feel uncomfortable, but it does mean that you shouldn't try to change who she is or manipulate her into doing something she doesn't want to do.
For example, if she starts seeing someone else after you two break up, it wouldn't be respectful of you to follow her or text her constantly. Even if you just think she might come back to you, this would be taking advantage of her feelings.
The more space she gives you, the more opportunity you have to show her that you're a trustworthy guy who won't abuse that power.