A basic set of 250 words are found throughout English text. These words are essential for fluent reading - they are the smaller words that are found in every sentence.
These words should be practised over and over until you can recall them almost instantly. This is called "deep memory" because they are driven into your long term memory, and are instantly recalled without thinking.
When these words are remembered and can be instantly recalled, they make the task of reading much easier, because you save your mental energy for decoding more complex words.