How to speak openly with people around whether family or friends?

i'm very bad at socializing???whether its a party or a family/friends gathering,, i dont seem to mingle with them. i always sit at one corner watching them enjoy,,scared to speak,,, thinking whether they may want to talk to me or not?????i'm a very good thinker than a doer!! till the time i gain confidence to speak ,,, situations have already taken place. this happens everytime...because of which my views always remains in my heart!! its so frustrating!!! has anyone experienced such a thing!! what can one do to improve oneself??