Hogwarts School of Witchcraft and Wizardry is the main setting of all the Harry Potter installments. With each of the students broken up by year and house (Gryffindor, Ravenclaw, Hufflepuff, and Slytherin) one of the only things all students have in common is the classes they take. Some classes must be taken by everyone and then there are elective courses that students are allowed to choose for themselves.
For diehard Potterheads, the dream is to attend Hogwarts. For many, the sorting quiz on Pottermore that allows you to learn your official Hogwarts house is the next best thing. If given the opportunity to attend Hogwarts, some classes would fill up and others would be skipped anyway.
TAKE: TRANSFIGURATION
Anything taught by Professor McGonagall requires attention. Transfiguration is one of the most important classes in the curriculum. It could also be considered a stepping stone to becoming an animagus. An animagus is a witch or wizard that can turn into a specific animal at will.
The process undergoes a long time to complete. Characters such as Professor McGonagall, James Potter, Sirius Black, and Peter Pettigrew all completed the transformation. It also comes in handy in other forms. Cedric Diggory used transfiguration to turn a rock into a dog during the first task of the Triwizard Tournament.
SKIP: HISTORY OF MAGIC
While learning about the history of the wizarding world is fascinating, Professor Binns was not an interesting enough teacher to bother taking the class. Students often fell asleep during his lectures. You would be better off borrowing books from the library or finding old newspaper copies.
History of Magic is the equivalent of muggle world history classes and there is a lack of practicing magic during the lessons. Unless you are interested in history specifically, it would not be the right class to take. It would be unlikely Professor Binns would even notice a student would be missing anyway.
TAKE: DEFENSE AGAINST THE DARK ARTS
Even with most of the professors being less than satisfactory, barring Professor Remus Lupin, this class also ranks as a deeply important one. Especially within the time of Voldemort and his followers, knowing how to protect yourself was an emphasized skill. This is proved during Harry Potter and the Order of the Phoenix when Harry, Ron, and Hermione create Dumbledore's Army.
During Umbridge's reign as Defense Against the Dark Arts professor and Senior Undersecretary to the Minister of Magic, she used her position to prevent the use of magic in classrooms, sticking to theories rather than active spell casting. Still, self-defense is valued, and would also be very useful during the Battle of Hogwarts.
SKIP: MUGGLE STUDIES
Muggle Studies is an elective class offered at Hogwarts. The class teaches young wizards about life in the muggle world. While the class may offer an interesting perspective, it would be more constructive to visit the muggle world itself and spend a day interacting with muggles.
For muggle-born or half-blood students Muggle Studies would be learning about a world they would or may already be familiar with, rather than the magical world they want to immerse themselves in. While knowing what wizards think the muggle world is like could have some merit, it would likely be skipped by students who are more interested in practicing magic.
TAKE: CHARMS
The ability to levitate objects or summon items to you are spells taught by Professor Filius Flitwick. While they may not be as known to be self-defense spells like Defense Against the Dark Arts, they do have an important purpose. Harry uses the summoning charm to retrieve his Firebolt during the first task of the Triwizard Tournament.
Without knowing that spell, it is likely that Harry would have come out of the first task much worse than he did. Knowing that charm was so important that Harry and Hermione stayed up late to practice it to ensure Harry could perform it perfectly.
SKIP: DIVINATION
Looking into the future could be interesting if you have the gift. Otherwise, it may feel like Hermione's viewpoint of the subject. Professor Trelawney leads her class through various exercises to teach them about prophecies and how to look into the future. However, often students did not understand what she was talking about and made jokes about her because of it.
Trelawney was a natural seer herself, having predicted at least two prophecies that would come true. Unfortunately, as a student, you may find yourself being told that something awful will happen to you.
TAKE: HERBOLOGY
Without Herbology, no one would know the importance of mandrakes. In Harry Potter and the Chamber of Secrets, a basilisk petrifies multiple students, including Hermione Granger. The mandrakes, a plant that would screech as it is pulled out of a pot, is also used as an ingredient to wake up the students from their petrified state.
In Harry Potter and the Sorcerer's Stone, Hermione remembers that Devil's Snare hates sunlight, another thing taught in Herbology. Hermione's memory of the lesson is what saves Harry, Ron, and herself from dying on their way to reach the Sorcerer's Stone.
SKIP: POTIONS
While Potions may be an interesting subject, Professor Snape was never a great teacher. Being in a classroom with him would only add anxiety to trying to get the potion correct. Potions is an art form that must be done exactly as stated in the textbook and therefore more difficult to understand and less likely to be as fun as other classes available.
Since potions are as specific to ingredients and instructions as one can get it is more difficult to get a correct final product. Neville Longbottom was well known to let his nervousness get the best of him and interfere with the potion quality.
TAKE: CARE OF MAGICAL CREATURES
Hippogriffs, Dragons, and other types of magical creatures appear throughout each installment of the Harry Potter series. Due to their constant appearance taking a class dedicated to understanding them would be a benefit. Instead of being frightened at seeing a creature you are not familiar with, this class would teach you how to interact with the creatures in a way that keeps both the person and the creature safe.
Having Hagrid as a teacher would only add to the class, as he was always excited about taking good care of the creatures he introduced to the students.
SKIP: ASTRONOMY
Taking Astronomy at Hogwarts is similar to how one would study Astronomy in a muggle school. Tracking the stars may be a relaxing pastime, but it is not known to be a truly magical class. Its formula is much too close to muggle science classes to bother spending the time to learn it in a magical school.
Rather than being a required course, it would be much better off as an elective. This way, those with genuine interest can attend and it would not be a problem for others who were not as interested in the subject.