Start out drawing the basic shape of the letters as if they were sans serif style.
Once you have the letters “ABCD” roughly drawn, go back over the letters to thicken those downstrokes. When drawing a serif type, be aware of the thick strokes versus thin strokes. Your downstrokes should be thicker. This adds to the classic, traditional feel of a serif font.
With a sharp piece of chalk, add the serif to the top and bottom of the strokes. For a different effect, connect the serif to the body of the stroke by drawing a small, curved, diagonal connector. This is called a bracketed serif and will give the letter a completely different look. This piece was excerpted with permission <a href="http://www.amazon.com/gp/product/0761186115/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0761186115&linkCode=as2&tag=craftfocom-20&linkId=DXXLIYGES62V5EZC">The Complete Book of Chalk Lettering: Create and Develop Your Own Style</a>.