How Does Someone Gain Your Trust?

I have asked this question of myself so many times in life but I have not managed to scratch the surface of how they would gain my trust. I cannot begin to understand myself and my unique feelings or dealings with people to begin to address such a question. I know the usual answers to such a question; Friends... never lie, don't hide the truth or mask it, do what they said they would do, admit their mistakes, are competent, show consistency and the like. But I do not always go by those specific determining factors. 

You see....

I come across as someone who easily trusts strangers with her feelings and past stories and on the flip side does not trust 'friendship bonds' so much. To me, anything can happen that would rock the foundation of a friendship despite our efforts to keep it standing. Situations might arise that thin out that bond which could either be patched up, or not, depending on how eager both ends want it back to the way it was. There are, however, friendships that whatever hole it fell into can survive by digging itself to the surface.

I love my friends and value their friendship so please do not get me wrong when I mention that there is an initial feeling that I get in my core from our first contact, be it a good one or not, which would help me make a decision about whether it is a friendship that I could trust in or not. It is kind of like first impressions really but with feelings. My senses are all involved, especially that of my heart, and those feelings linger on for a long time before they either fizzle out or are proven correct. 

Like I mentioned above, I cannot begin to understand myself. Having said that it is more often than not that these initial feelings are proven correct. I am never sure what that 'friend' says or does that sends my heart and brain small signals that either send me a green light to go ahead and trust or warn me against fully trusting them.

I have a hard time trusting people if these warnings continue to buzz, ring or jingle as I seem to focus on how they would hurt me, when I should expect that hurt to arrive and on which boat. However, when my heart gives me the green light, I trust wholeheartedly without any hesitation afterwards. 

If, on the odd chance, my initial feelings were incorrect, then I fall flat on my face and hurt for a long time as it would if there was a prickly pear thorn on my finger tip; I may not see it but I can feel it. I feel hurt either way; whether I was right or wrong.  

What about you? Can you answer the above question with ease?