Once you have the basics of a few calligraphy hands down, it's natural that you would want to be able to embellish them a bit. Flipping through books of old manuscripts and looking at modern invitations and announcements are great ways of getting ideas, but nothing beats good, old fashioned practice. Knowing a few things about the general form and purpose of flourishes helps too. Flourishes can be used around single letters, at the end of a line of calligraphy to take up space (to justify the line rather than hyphenate the next word) or at the end of words or documents as a subtle form of punctuation. Here are ways to create flourishes for your calligraphy.
The basic flourish shape is a figure eight, ribbon or infinity loop. Practice this until the motion becomes smooth and natural. Notice how the sets of loops run parallel to each other and the width of each level can expand and contract. Work with plenty of arm room and move your entire arm through the flourish instead of just your wrist to get the most natural line shapes.
Flourishes should be a natural extension of the letter they extend from, so use them with the more flowing hands where serifs are a natural jumping-off point for the flourish as opposed to more angular types.
Use two pencils held together (creating a double point) to duplicate the thick and thin nature of a furling ribbon. Ink over these lines in one color and fill in with another for a two-tone effect or leave the bare pencil for a simpler look.
When using a metal calligraphy nib, press gently on the upstrokes to avoid gouging your paper or splattering ink. Apply firmer pressure on the down strokes to take advantage of gravity and varying line widths.
Flourishes can surround a single letter to create the look of a monogram when alone on a page or to suggest a more illuminated look at the beginning of a paragraph or document.
Individual lines can be used in a flourish--the art is not limited to continuous figures. Explore extending the crosses of t's, h's or other letters to act as base lines to flourish around.
Practice a lot on scrap paper before attempting flourishes on a finished piece of calligraphy to save having to redo all your hard work. The standard order for a three-letter monogram is first-last-middle for a single name or man's first initial, shared last initial and woman's first initial for a married couple's joint monogram. The center letter is generally enlarged to show importance.