Wishes

Use the subjunctive when you want something.

Examples:

Quiero que este café sea más dulce.
= I want this coffee to be sweeter.

Ojalá que tuviera una casa más grande.
= I wish that I had a bigger house.

Emotions

Use the subjunctive when you're expressing an emotion.

Examples:

Me alegro de que te guste.
= I'm glad that you like it.

Me molesta que el esté tan orgulloso.
= It annoys me that he is so proud.

Impersonal Expressions

Use the subjunctive when there is no particular person in the subject.

Examples:

Es extraño que no haya nadie aquí.
= It's strange that there is no one here.

No era necesario que hicieras eso.
= It was not necessary for you to do that.

Recommendations

Use the subjunctive when you are suggesting something.

Examples:

Te aconsejo que escapes ahora.
= I advise you to run away now.

Te sugiero que no hagas eso.
= I suggest that you don't do that.

Doubts

Use the subjunctive when you are expressing uncertainty.

Examples:

No creo que sea una buena idea.
= I don't think that it's a good idea.

No parece que estés listo para este examen.
= It doesn't look like you're ready for this exam.