I would say that if you can guess the word's meaning from the context, write down the word and continue reading the article. After you finish, look up the word in the dictionary and write down its definition. If you have to stop a lot to look up words, you might not get through the whole article. I think that reading as much as you can will help you to understand the context of English writing best. Good luck!

Look the words up in a dictionary. Don't guess. Guessing is for when you don't have a dictionary handy. And even then, if you're going to guess, at least have a good knowledge of Greek and Latin root words to make an educated guess. For example, if you know "aqua-/aque-" means water, then a word that includes it MIGHT have something to do with water. (A lot of words in English have origins in other languages.) Also, when you read an article in English, are you just reading it silently? If you are able to, read it aloud to check your pronunciation. You don't want to learn a lot of new vocabulary and then not be able to use those words in a conversation.

The easiest way to learn new words is by keeping track of which words you don't know. When you read, watch TV, or listen to the radio, make note of words that seem new to you. Later, when you have more time, look those words up. A word that you got wrong or didn't know will be much easier for you to remember later if you apply conscious effort than one someone just gave you at random. Break it down: Never try to memorize more than 7-10 new words in a day. Our brains are designed so that we can only hold 7 things in working memory. Once you've incorporated those 7 words into your long term memory, you'll be ready to learn 7 more. Group them: While it's true that you can't learn more than 7 things at a time, there is a way around this. When you group things together in your mind, they take up less space. So for example, if you learn the words ebullient and exuberant together, you will remember them together, and they will only take up one slot in your working memory. Try to generate vocabulary lists that focus around single themes, emotions, or experience to take advantage of this phenomenon. Write sentences: It is crucial that you don't just memorize the dictionary or textbook's definition of a word but that you really incorporate it into your own way of understanding things. For this reason, it's helpful for many people to write sentences out for new words that they are learning. These sentences are also helpful later for reviewing because when you read your own sentences, you activate the schema you tapped into in the first place. If you don't have the time or inclination to write out sentences, try to at least use the words in conversation a few times within a day of when you learn them. you can do it! :)

If you do most of your reading online, you will do yourself a big favor by installing a tooltip/popup dictionary. That allows you to hover your mouse over any word and get a popup of the definition.

Look them up in the dictionary, and write them down over the word in the article you are reading! Guessing is overrated!