Linking words are promises, not decoration
"However" promises a contrast is coming. "Furthermore" promises an additional point in the same direction. "Therefore" promises a conclusion follows logically from what you just said. If the sentence after the linking word doesn''t keep that promise, the writing feels confusing even though every individual sentence is grammatically correct.
Four jobs, four families
Addition: furthermore, in addition, moreover — adds a same-direction point. Contrast: however, on the other hand, whereas — signals the opposite direction. Cause and result: therefore, as a result, consequently — a conclusion that follows from prior evidence. Example: for instance, for example, to illustrate — a specific case supporting the general claim just made.
The most common mistake
Using "however" and "moreover" as generic paragraph-starters regardless of whether a contrast or an addition actually follows. Before you write a linking word, finish the sentence in your head first, then choose the connector that honestly describes the relationship between the two ideas — not the other way round.
Practice
Take a paragraph you have already written. Cover the linking words. For each one, guess what relationship you think used to be there, then check your original word choice against that guess.