For designing a better ad, is it recommended to use bold font, different types of fonts, only one... Which one will be less dodged in a web site?
If all you've got is text, then use different sizes and weights to make the most of the space.
What one or two words will grab the attention of the casual reader? Put that in big, bold type at the optical center of your advert (i.e., slightly above the physical center). EXCEPTION: If it's a small newspaper or magazine advert, put the grabber text at the top, because that's the convention for those media.
Arrange supporting text above and below the grabber in smaller sizes according to importance. Don't overwhelm the reader. Only say what's necessary.
Don't consume all the space. Black text floating on a white background is more effective than the grey appearance of a white space (e.g. a monitor screen) filled with text.
Make sure that people know how to get what you're selling by putting that information in type that's smaller than the grabber type, but larger and bolder than the supporting type. Put the how-to-get-it at the bottom, where people will look for it.