Any suggestions on how to discipline a 3 year old? The time out isn't working at all...?

She just seems to be getting more, oh what is the word i am looking for, oh yeah BRATTY!!!! She is my only living child, I lost my son to prematurity 5 years ago, so my husband and I do spoil, but I cant take the bratty acting... Now she is much smarter, than a average 3 year old. and alot more mouthy in the sy department also... I know it is from being around grown ups... Next year she goes to Pre K.. But I need ideas to make her realize, she just cant act any and every way she wants, also, is this normal for 3 year old's......?