For some, teaching vocabulary is considered antiquated and meaningless, but there is a place in the current minds of students for learning vocabulary. Why? Learning new words is never a bad thing. Sometimes you can even amaze students with the variety of words that you actually know! Teaching vocabulary can be a bad thing. There is a right and wrong way to include vocabulary in a Language Arts or English classroom.
First, as with everything in your classroom, vocabulary has to have a purpose. Reading The Odyssey? Include some vocabulary that is used in the text that you feel might trip students. You can use other, smaller texts as inspiration for your vocabulary choices. Picking random difficult words for the sake of Doing Vocabulary makes it seem pointless, even if you have some sort of assessment over the words.
Next, too much is a bad thing. It's pointless to attempt to teach kids ten, fifteen or twenty words at a time. Forcing that many words, especially if they are of the random variety, will result in nothing more than rote memorization with the students abandoning the words by the next week, if they bothered to learn them at all. Three to five words is about the most you want to give. It doesn't sound like a lot, but they are more likely to take the time to learn a smaller number of words and, more importantly, remember them.
If you don't have a text you're reading or words you can draw from, make the vocabulary useful in some other way. I teach Greek and Latin Roots, which I have linked here if you'd like them. Why do these work? Roots are like the puzzle pieces that help build words. Sometimes students run into words that they don't recognize. By teaching them roots, they can use this knowledge to help figure out the meaning of words they might stumble over.
Vocabulary is a valuable part of the classroom. The problem is that sometimes it can be seen as a useless part of education by students. In giving vocabulary a purpose and decreasing the amount of words, vocabulary can be less annoying and more useful for teachers and students.