Perhaps it is the word you never seen before or just forgot what the word means again.
If you have this trouble, don't be nervous, and please don't look up the word in dictionary right away.
No matter you're reading your text books, or newspaper, you can guess the meaning of the word by the context
When you read an essay or article, the writer used a word which might be difficult, such as some specialized words
let me take this word "anthropologist" as an example.
If you read an article, and you find this word, and you dont understand it, dont worry about it, read on.
anthropologist, a person who studies human beings.
anthropologist, that is, a person who studies human beings.
anthropologist−a person who studies human beings.
if that specialized terms is followed by just a comma, "that is", a dash"--"
those mean that the following sentence is going to explain what the word is.
If you want to understand what the news is, the headline and the lead(the first paragraph of news)is the most important, and the following paragraphs just show you some details--if you wanna know more about the story, just read on.
So, for the lead of a piece of news. First, you have to find out the subject and the main verb, in this way you will know what the story is.
a relative clause(begin with "which or who, etc") or participle sentence(begin with present participle "V+ing" or past participle "V+ed")
these two kinds of sentences, just an addional information, saying what the subject is. so don't search for subject and main verb in these two types of sentence.
However, if the subject or main verb is the word that you don't understand, you might need to look up that word.
but, disunderstanding word, please guess it from the context first.
suggestions above aid to improve reading skill
you could write down words you dont know to your note book or something to memorize them.
and for upper level, you can try to study prefix and suffix and root of a word