As an intermediate English learner, understanding the general meanings of a word is not enough if you want to achieve to a higher position. Understanding exactly is required. Have you ever experienced such situation; when you encounter a word in reading, you just understand it by translating its meaning from your native language. If so, it means that you just understand the general meanings of this word. On the other word, you have lost many detailed information of this word. You should be aware of this situation. Otherwise, you will be stuck in intermediate level if you ignore such situations.
What's your ideas?
I think it depends on your level. At C1, you really want to look up every word to build vocabulary and get the nuances. If you are in B-territory, I would stick to words which appear repeatedly in the text or which seem to be crucial to understanding the progress of the story (but leaving out occasional random adjectives and the like) - otherwise, it can slow down the progress of reading too much and lead to frustration. Like Ela said, e-readers are a great help if they have a built-in dictionary. Ultimately, it is a question of how many words per page and how long it takes you to look them up. If you are down to 2-3 words per page I would look up every one of them, if the number is much higher I would stick to the ones that seem most important.
E-book readers are great just for that.
When learning a language, it really helps to be able to take a large word appart into smaller words that are often used in other big words (uni-, trans-, un-, im-, etc.).
And learning the origin of a word (especially for a Language like English whose origin is mixed) can be helpful when you're learning your next language!
For example you may assume or roughly translate "to hop" as meaning "to jump", which would be correct, but it refers to a particular kind of jump.
You could not use it in place of "jump" in every situation.
Keep looking those words up Lawrence!