How do I know when to use the subjunctive mood? - A Level question

One of the easiest ways to spot whether you might need the subjunctive is when you see the word 'que', as this usually comes after phrases which trigger the subjunctive.Of course, this word is used a lot in French so it doesn't always mean you have to follow it up with a verb in the subjunctive mood. However, if you then think about what the sentence is trying to say and you see that there is an element of doubt, emotion or necessity in the phrase - for example "Il faut que..." meaning "It is necessary that..." - then you'll need the subjunctive.So if you were saying "Je pense qu'elle est gentille" (I think that she is kind), you would use the indicative mood (just the normal present tense we are used to seeing).But if you wanted to say this in the negative, "Je ne pense pas qu'elle soit gentille" (I don't think that she is kind), you need the subjunctive because there is an element of doubt and judgment in what you are saying.