First Letter Mnemonic
Take the first letter of every star type, and create a memorable sentence with those letters. So the star types protostar, T tauri star, main sequence star, red giant star, white dwarf star, red dwarf star, neutron stars and supergiant stars would have the first letter sequence of ̶0;PTMRWRNS̶1;. Something like ̶0;Put The Milk Right Where Roger Neutron Says̶1; would be a memorable way to recall all the different letters.
Loci Method
The loci method is a slightly more complicated memorization technique. You start by imagining a room that you are familiar with, like your bedroom, for instance. You then go and, in your mind, place each kind of star that you have to remember in a different location around the room. Later, when you want to recall the different stars, you imagine yourself going back through the room and taking those stars back down from where you previously placed them.
Pegword Method
With the pegword method, you start out by memorizing a sequence of easy-to-remember items. Words that rhyme with numbers, for example, such as bun for one, shoe for two, tree for three, and so on, is one good method. Then you associate the things you want to remember with the items you have memorized. You might imagine a white dwarf star in the shape of a bun, for instance. Then, when you recall the list of memorized items, the associated star will spring to mind.
Flashcards
There are many ways to memorize things, and the standard methods can work well, too. Flashcards, for instance, are a great way to memorize things. You could put a picture or description of a given star on the front of the flashcard and then the name on the back. After looking at the picture or reading the description, you test yourself on whether you know the name. You can then check your answer by flipping over the card.