I think everyone has already covered the recommendations well. Find you a good permanent finish that you like. A good place to start is the Finishing section of the Library. You can practice a new finish on any cheap wood. Looks like your turning technique is pretty good - nice level turn which is hard for a beginner to master, most have some curve to them.
The two main areas most of us notice from a technique standpoint are fit next to the hardware and the finish. To move up, be ruthless on matching the diameter of your hardware and calipers are a must for the best work. They don't have to be expensive, but skip the plastic ones. Harbor Freight has a very nice one, almost always on sale for about $10. Measure the diameter of the tip, lock the caliper at that diameter and then use it as your test for when you have turned to the correct mating diameter for that end of the tube. Depending on the thickness of your finish, the caliper should slide easily onto the wood when you are "there". Obviously if you are doing plastic, you might want a closer fit because you don't have a finish to build up.
When learning, buy extra tubes. You don't have to assemble every attempt if you don't like the way it turned out - although it doesn't look like you will have many to throw away. Nice start!
Harry