The best way to solve this problem is to draw out a logic puzzle grid. See this page for an example of what this grid looks like: http://www.logic-puzzles.org/game.php?u2=96bddb511786e45642dd1127f2719fea
There, you can see how there are "categories"-- in the example, the categories are Names, Countries, Years, and Heights. In your puzzle, the categories will be Friends (Wolfman, Frankenstein, etc.), Costumes (Cinderella, Papa Smurf, etc.), Items (pumpkins, apples, etc.), and Order (1st, 2nd, 3rd, 4th).
First, draw the three lefthand boxes of your grid with (top to bottom) Friends, Costumes, and Items. Within the "Friends" category, you will have a row for Wolfman, a row for Frankenstein, and a row for each of the other two monsters. (Four rows in total in "Friends.") Within "Costumes" you will have a row for Cinderella, a row for Papa Smurf, and a row for each of the other two costumes. (Four rows in total in "Costumes.") Same for items-- one row for each of the items, for a total of four rows in "Items."
Then, draw the three boxes across the top with (left to right) Order, Items, and Costumes. Within "Order," you will have a column for "1st," a column for "2nd," a column for "3rd," and a column for "4th." Then the labels for Items and Costumes will repeat, but this time they will each get a column instead of a row.
(You will see that there is no overlap between the same categories-- as in the example, Countries doesn't overlap with Countries, and Years doesn't overlap with Years.)
Now, you need to read through the clues and put "x"s in your grid when you have eliminated a possibility. For example, if you know that Wolfman did not come dressed as Tinker Bell, put an "x" in the box where the Wolfman row intersects with the Tinker Bell column to show that you have ruled out that combination.
So, then you might ask, how do I use the clues to narrow down the possibilities? Let's look at the first clue. It says, "The monster dressed as Papa Smurf arrived just before the Creature from the Black Lagoon, who arrived sometime just before the monster who brought the pumpkins for the guests to carve into jack-o'-lanterns."
This tells you a lot of information!
1. The Creature from the Black Lagoon did not dress as Papa Smurf, and the Creature from the Black Lagoon did not bring pumpkins. So go to the row for the "Creature from the Black Lagoon," go across to where it intersects with "pumpkins" and "Papa Smurf," and put an "x" in each of those boxes.
2. The monster dressed as Papa Smurf did not bring pumpkins. Go to the row for "Papa Smurf," go across to where it intersects with "pumpkins," and put an "x" in that box.
3. Papa Smurf arrived before the Creature, who arrived before the pumpkin-bringer. This means...
(a) Papa Smurf did not arrive 3rd or 4th (because he needed to have two people arrive after him). Go to the row for "Papa Smurf," go across to where it intersects with "3rd" and "4th" and put an "x" in each of those boxes.
(b) The Creature did not arrive 1st (because Papa Smurf was before him) but also did not arrive 4th (because the pumpkin-bringer was after him). Go to the row for the "Creature," go across to where it intersects with "1st" and "4th" and put an "x" in each of those boxes.
(c) Finally, the pumpkin-bringer did not arrive 1st or 2nd (because at least two people arrived before him). So go to the row for "pumpkins," go across to where it intersects with "1st" and "2nd" and put an "x" in each of those boxes.
The second clue is very similar, in terms of telling you a monster, an item, and a costume. Work through that clue to figure out what possibilities it eliminates, just like I demonstrated with the first clue.
The third clue says, "The four monsters are, in some order: Frankenstein, the one who brought his CD collection (which included "Monster Mash"), the one who wore a Peter Cottonail costume, and the third monster to arrive."
For this clue, you just need to work through and cross-reference everything. It tells you:
1. Frankenstein did not bring his CD collection, did not dress as Peter Cottontail, and was not third. Put an "x" in each of those boxes in the Frankenstein row.
2. The one who brought his CD collection did not dress as Peter Cottontail and was not third. Put an "x" where the "CD collection" column crosses the "Peter Cottontail" row, and an "x" where the "CD collection" row crosses the "3rd" column.
Eventually, as you work through clues, you will reach a point where you will have 3 "x"s in one category-- for example, you might have shown that the Thing did not bring CDs, the trivia game, or apples. This will leave one empty space, meaning that the Thing must have brought pumpkins. When you get to this point, put a "O" in the remaining box (in this example, it would be the box where the "Thing" intersects with "pumpkins".) Once you get an "O," cross-reference what you already know. For example, if you know that the monster who brought pumpkins did not arrive 1st or 2nd, now you also know that the Thing did not arrive 1st or 2nd. Mark those boxes if they aren't already marked.
If you've worked through all the clues and haven't reached a final solution, go back and read the clues again to see if there's something you missed.