Actually, it's a very tricky question (which makes me think most people suggesting to read a book did not give it much thought). Many different trains of thought depending on what trade you are putting on. In the end, it's about comparing risk and reward broken down into risk factors of your strategy.
For example, breakeven terminal price is the simplest - take you strike, add the cost of the option and decide if you think the underlying will breach that level. E.g. you are buying a call and think you gonna hold the trade to expiration, you are risking the premium and hoping to collect a reward that's bigger (because you think the market is misjudging the terminal distribution of the stock, if you want science-speak).