When I first meet someone, and I get such warnings, I'll tell them in subtle ways. For instance "becareful, drivers can be crazy at night", "hey, why don't we go this way, that street is too dark", "maybe you should move that glass, its too close to the edge of the table and could fall". I look like the worrier, but it's easier to reason with someone than tell them you're intuition is telling you something. Eventually, after knowing me long enough, they begin to listen to me because they realize my "instincts" are correct, especially after they see how often I'm spot on. They won't come out and say anything directly about it, but they usually start coming to me for advice and telling me private information, despite how little we know each other.
Use your gift to help others, but learn to recognize it before relying on it. Right now you can't recognize it as anything more than passing thought. Only you can observe yourself and learn to recognize the difference. Once you do, it will be a wonderful tool. But remember, we are not perfect, the future isn't written yet, and we won't always be right, so use your common sense and don't do anything foolish. We sense these things because we tap into the interconnectedness of all things, what I call the web of life. We are all connected, therefore we are all capable of doing this, however few actually take the time to listen.
By the way, it can also be used to decipher present circumstances and is actually far more accurate that way, all you have to do is focus on it with an open mind and pay attention. I suggest picking up scrying, tarot or the runes to help train your mind.