When I started, I had already had some years experience in woodworking and finishing, but that didn't help that much in the tiny area of making a pen. I made my first three or four, then cut a piece of a 2X4 pine into about 10 to 15 blanks and made a day of learning to drill small pieces of wood, gluing tubes in, turning them down and then learning to finish. I was not trying to make a pen, but rather getting the feel of each part.
At that time, I had drilled holes in wood for nearly 60 years in making things, but drilling holes lengthwise in 3/4 by 3/4 by 2 inch blanks was quite different. Drilling in 3/4 by 3/4 can make one that thin blow out or go sideways. Turning a pen blank to size that is only 3/4 inch is quite different than turning a 4" to 8" square or round wood. Very little room for error plus the speed (RPM) for 3/4" blanks is different from turning bowls or vases. THEN getting the pen blank to the correct size is another thing. Learning how how much to turn and how much to sand with what grit. One error is getting it down to size with a 120 grit and then trying to sand the 120 scratches out with 220 up to 400 and you have sanded it way down past the bushings.

DAKHIKT!
Add to that the fact that one has purchased a nice piece of wood that makes it scary that you are about to waste, . . . the best thing to do is cut some 2x4 pine and practice for a few hours. Then with getting that experience of just 5 or 10 practice blanks, you would be surprised how much you have learned and progressed!
One suggestion will be to get a set of calipers and learn from the beginning to measure the size of your blanks as you turn. Bushings will shrink as you hit it with the chisel or sand paper. Measure the nib end, the center band and the clip end and turn the blank to fit that, not to the size of the bushings. This will make for much better fittings.