How do I know when to use the subjunctive in Spanish?

In Spanish there are four main ways in which the subjunctive is used.

1. Formation of the negative imperative and the formal positive imperative

The exception here is no creer que

2. In subordinate clauses introduced by que

In this instance there are certain expressions and verbs which require a following subjunctive. These are:

a) After expressions which indicate possibility, such as es probable que

b) After expressions and verbs that express an emotion, such as querer or es una pena

c) After expressions and verbs that indicate necessity, influence or requests, such as es importante que or pedir

d) After verbs which indicate something is allowed or forbidden, such as dejar or prohibir

e) After verbs which involve thinking or saying BUT in the negative, such as no creer or no parecer

3. After conjunctions

The subjunctive in this case is generally used with conjunctions of time and purpose:

a) Time conjunctions-cuando, hasta que, en cuanto, mientras

BUT only use the subjunctive if the tense communicated after is in the future

ALSO if cuando is used in a question use the indicative

b) Purpose conjunctions-para que

4. In main clauses

The subjunctive is used mainly after perhaps EXCEPT for a lo mejor