Shyness vs openness..?

im kind of shy when it comes to meeting new people. itend to stumble over words and not know what to say besides 1 or 2 words.. there r guys i meet n i like them n they like me but sometimes there r those guys with so much personality that it like bears over me n i feel so out of place like i cant keep up with conversation n i feel like they wouldnt be interested in what i have to say bc they r so overbearing when it comes to conversation so i just keep quiet.. so i just want to know has anyone ever met someone with such a strong personality that u feel intimidated(i guess thats the word to use) n if so what do u do to overcome this how can i just open up and be myself??