Avoiding ghosts
When you do not want to be hit by ghosts and lose all your items (Balloons, Beans, and sometimes Stink Pellets) just stand on the ledge until the specter nears you. Tap the controller so that you will fall and catch the ledge. When you are hanging, they cannot hit you and cause your items to go flying.
Bertie Botts Bean Bag (100 Bean capacity)
Use the Skurge spell on a chest covered in ectoplasm behind a tapestry (you need the scissors spell) on the third floor, by the Defense against the Black Arts classroom.
Bertie Botts Bean Bag (200 Bean capacity)
Gather every item for the students around Hogwarts (not the Notice Board). You have to actually find the people. The final person will give you a key to the confiscated items room. In there are six Wizards cards and the biggest Bertie Bots Bean Bag.
Defeating the Giant Mother Spider
To get to it, use your Lumos spell to light the floor and follow the trail of spiders. Unlike the book, the spiders that are not normal size will try to kill you. Attack them with Incendio. When fighting the Giant Mother Spider, do not try to hurt the spider itself. Instead, use your Incendio spell to burn the web it has attached to the various trees. When done, it will fall into the pit and you will slip in after it. In here, just run around until it rears its head and exposes its soft under-belly. It is the only part that is susceptible to second level magic. Note: It is best to not charge and use rapid firing to get a little extra damage.
Defeating the Giant Mother Spider 2
While fighting it, you may notice little sacks being dropped and suspended by webbing. Shoot them down with Flapendo and collect health and Bean power ups from Hedwig.
Defeating the Giant Spider
To defeat the Giant Spider in the Dark Forest, circle around him and cast Rictosempra. He will not shoot any spider webs at you.
Easy Sickles
Once you have collected your Standard Book of Spells (Grade 2) in Diagon Alley, you can cast Flipendo to break barrels and uncover Sickles that you can use to buy items such as Stink Pellets at Gambol and Japes.
Expelliarmus Challenge
Use your spell that cuts down tapestries and ropes on the spiked ball. Walk up close to the edge and hold your trigger button, charge up for a half second and cast. Note: If you throw the imps into the fiery pits, they will die and you do not have to worry about them. Likewise, if you throw them all away you cannot put them into the cages to get out; but when all are indeed gone, they respawn from that hatch in the wall at the first ramp.
Forbidden Forest spiders
The spiders in the forest act as follows:
Tiny Black: Show you the path
Big Green: Jumpers (jump, run away, and jump again)
Big Red: Flingers (they spit)
Big White: Flingers (spit paralyzing venom)
Big Multicolor: Possible Jumper/Flinger mix.
Nimbus 2000 Broomstick
On the second day of school, go to the Quidditch practice. Complete the training with a "B" or better rank to get the Nimbus 2000 flying broomstick. You can now fly anywhere around the school during the day. Note: You can only land on grass and cannot fly inside the school.
Personal Requests and Notice Board
The Notice Board in the Gryffondor common room usually gives a location, but higher up as you near completion they start to give vague clues, such as "Could be anywhere on grounds". With personal requests, they do not ever really give you a clue, except the first one. However, the items are near the area in about a two acre search range.
Sneaking around at night
When sneaking around at night, you need to get by many of the prefects. When you need to get by them, simply crawl under the bookcase to the left of the portrait that leads to the Griffondore common room. It leads through a secret passage that takes you to the fourth floor. When sneaking around and you do not want to walk slowly, you can use various objects and spells to distract the prefects. Stink Pellets are not too reliable, but the non-explodable luminous balloons work well. As for spells, try Flapendo.
Transformation spell
After you acquire the spell and return to the main room, use it to get across the room on the other side of the gargoyle. You will need to use the hardly visible ledges to cross. Hang off the wall ledge to escape nearing ghosts, and push down the slabs to make a bridge. Once this is done, you will have to fight the gargoyle. It is recommended that you get on the right staircase, halfway up. Then, use the spell on the last stone and the door will open.