Don't know if you remember the Byrd's song "Turn Turn Turn" but my advice is to do just that!

After you make three or four pens, get a piece of 2x4 and made 8 or10 blanks from that and practice drilling, practice turning to a particular size, get the feel of the tool of your choice, get the feel of the wood with the tool, practice sanding and get the feel of sanding while the blank is turning. Waste a small bottle of CA learning to apply it and sand it.
That will give you more experience that 20 pens. Oh and buy and use a good set of calipers. Measure the nib end, center band and clip end. write those numbers down. Turn to size by checking with the calipers to match the size of the fittings. Don't rely on the bushings for sizing.
Use SHARP tools. Learn how to sharpen your tools and sharpen them regularly, OR use a tool with carbide inserts if you are unfamiliar with sharpening. Carbide inserts are replaceable and they stay sharp longer than HSS tools. (But for those skilled, HSS can be honed a bit finer than carbide.)
A link that is old but still relevant:
http://www.penturners.org/forum/f14/if-i-had-known-earlier-46654/