There is nothing more aggravating than reading some dialogue and not being sure who is speaking. So, unless you have two characters who are diametric to each other—say, a Valley girl and a Eighteenth Century vampire—be sure to add tags to dialogue. Sooner is better than late!!! Add your tags after the first sentence or first clause.
“Oh, Dracula,” the bimbo said, “you sure have an awesome crib. I can totally get real here.”
“My darling, girl,” the Count said. “Your exuberance is most gratifying.”
Okay, so this is not exciting dialogue, but it is clear, you know who is speaking and a picture is beginning to form in you mind.
Special Hint: Writing a scene with two wildly different characters is easier and more interesting.