The Subjunctive Simplified
At the risk of being beheaded here by the purists I would like to share a simple trick that solved the subjunctive for me.
I read all about it not being a tense but a mood and expressing a desire or feeling - it didn't help.
My new teacher when he spoke in the subjunctive merely streesed QUE long and loud when he was going to use the subjuctive.
Now if I have QUE in a sentence it is a flag for me that it is possible that I should be in the subjunctive:-
Es possible QUE este en el subjunctivo.
Now of course some QUEs are not subjunctive but the list is much shorter than those where "the trick" applies.
Here we get the flag QUE but stay indicative:-
creer que ... to believe that ...
no dudar que ... to not doubt that ...
es cierto que ... it is certain that ...
es claro que ... it is clear that ...
es evidente que ... it is certain that ...
es obvio que ... it is obvious that ...
estar seguro que ... to be sure that ...
es verdad que ... it is true that ...
no cabe duda que ... there's no doubt that ...
no es dudoso que ... it is not doubtful that ...
no hay duda que ... there is no doubt that
Here we get the flag QUE and slip into the subjunctive.
a menos que ... unless ...
antes (de) que ... before ...
con tal (de) que ... provided that ...
cuando ... when ...
conviene que ... it is advisable that ...
después (de) que ... after ...
dudar que ... to doubt that ...
en caso de que ... in case ...
en cuanto ... as soon as ...
es aconsejable que ... it's advisable that ...
es bueno que ... it's good that ...
es difícil que ... it's unlikely that ...
es dudoso que ... it is doubtful that ...
es fácil que ... it's likely that ...
es fantástico que ... it's fantastic that ...
es importante que ... it's important that ...
es imposible que ... it's impossible that ...
es improbable que ... it's unlikely that ...
es incierto que ... it's uncertain that ...
es increíble que ... it's incredible that ...
es (una) lástima que ... it's a pity that ...
es malo que ... it's bad that ...
es mejor que ... it's better that ...
es menester que ... it's necessary that ...
es necesario que ... it's necessary that ...
esperar que ... to wish that ...
es posible que ... it's possible that ...
es preciso que ... it's necessary that ...
es preferible que ... it's preferable that ...
es probable que ... it's probable that ...
es raro que ... it's rare that ...
es ridículo que ... it's ridiculous that ...
estar contento que to be happy that ...
es terrible que ... it's terrible that ...
hasta que ... until ...
insistir en que ... to insist that ...
mandar que ... to order that ...
más vale que ... it's better that ...
mientras que ... while ...
negar que ... to deny that ...
no creer que ... not to believe that ...
no es cierto que ... it's not certain that ...
no estar convencido de que ... to not be convinced that ...
no estar seguro de que ... to not be sure that ...
no es verdad que ... it's not true that ...
no imaginarse que ... to not imagine that ...
no parecer que ... to not seem that ...
no pensar que ... to not think that ...
no suponer que ... to not suppose that ...
ojalá que ... if only he would ...
para que ... in order that ...
pedir que ... to ask that ...
preferir que ... to prefer that ...
prohibir que ... to prohibit that ...
puede ser que ... it may be that ...
querer que ... to want that ...
recomendar que ... to recommend that ...
rogar que ... to plead that ...
sentir que ... to regret that ...
sin que ... without ...
sugerir que ... to suggest that ...
tan pronto como ... as soon as ...
temer que ... to fear that ...
tener miedo de que ... to be afraid that ...
It may not be pure but it worked for me !
10 Answers
My new teacher when he spoke in the subjunctive merely streesed QUE long and loud when he was going to use the subjuctive.
Unfortunately, the subordinate clause does not always begin with "que". You will see ojalá used without the "que" and the subjunctive is still required or with some adverbial clauses.
Lo haré cuando nos levantemos. I'll do it when we get up. [Subjunctive]
The subjunctive is used when the cuando clause refers to future time. Notice that there is no "que" in the sentence.
So "que" is a possible flag (but not a reliable one) and there is no simplifying the subjunctive. It is a complex mood for English speakers to master.
No se puede estudiar bien en una postura incómoda, en un lugar mal iluminado o en una habitación donde haya personas hablando.
Indefinite or non-existent antecedent...requires the subjunctive, but no "que"
Well I think you were very brave, je je 
It's great to try to help others understand such an involved and often tricky part of the Spanish language - after all if your tip helps you and you want to help others, good on you for sharing.
However, as the others have ably pointed out there are going to be times when your tip won't work. You might be safer limiting the description a little, presenting it as an aid to 'one of the aspects' of the subjunctive or something along those lines instead of 'solving' the whole dealio but there is definitely value in what you've shared and hopefully the other comments here have helped you understand the subjunctive a little more too - after all that's why we're all here, to help and be helped learn Spanish! 
When it comes to grammar, any "rule," "rule of thumb," "flag" or "trick" will lead you astray if thoughtlessly applied all across the board. This site is rampant with rules and exceptions to those rules and endless debates about whether any of the rules are valid in the first place. Just check out all the References and Answers regarding Ser vs Estar! Roger made it pretty clear that this is only a flag that should make one stop and ask, "Are we headed into subjunctive territory here... or not?" "It's possible" is the only claim he makes.... (well, OK, his title is a bit misleading and Kiwi makes a very good point about that).
Anyway, I, for one, will take any and all the help I can get, knowing that the final decision rests on me and my entire repertoire of acquired knowledge. One thing will never be in doubt..... I'll have to use "every trick in the book" to navigate in Spanish. Good tip Roger!
It's the idea of a doubt (incertainty) that carries the need of the subjunctive.
You should really forget about this "rule"
Creo que no voy a cine hoy.
Expressing doubt....right?
No tengo ganas de que vengas a mi fiesta.
Any doubt here?
Indefinite or non-existent antecedent 
as I said at the risk of being beheaded by the grammar police.
It's not a rule - it's a flag that has helped.
All the fancy talk is way over my head - it's just a flag that I have found useful for some aspect of the subjunctive.
I could not understand English if we talked about antecedents and antipersperants, and subordinate subversive clauses.
Maybe this will help clarify things. This is from a Wikipedia article on the Subjunctive Mood: "In grammar, the subjunctive mood ..... is a verb mood typically used in subordinate clauses to express various states of irreality such as wish, emotion, possibility, judgment, opinion, necessity, or action that has not yet occurred."
"It is sometimes referred to as the conjunctive mood, as it often follows a conjunction. The details of subjunctive use vary from language to language." (my italics)
In the discussion of the Spanish subjunctive, the author goes on to say this about the present subjunctive.
When to use: When there are two clauses, separated by que. However, not all "que" clauses require the subjunctive mood. They must have at least one of the following criteria.
- As the fourth edition of Mosaicos states, when the verb of the main clause expresses emotion. (E.g. fear, happiness, sorrow, etc.)
- Impersonal expressions are used in the main clause. (It's important that...)
The verb in the second clause is the one that is in subjunctive!
Examples:
- Ojalá me compren (comprar) un regalo. (I hope that they will buy me a gift.)
- Te recomiendo que no corras
(correr) con tijeras. (I recommend
that you not run with scissors.)- Dudo que el restaurante abra
(abrir) a las seis. (I doubt that the restaurant might open at six.)- Lo discutiremos cuando venga (venir). (We will talk about it when he/she comes.)
- Es importante que (nosotros) hagamos ejercicio. (It is important that we exercise.)
- Me alegro de que (tú) seas mi amiga. (I am happy that you are my friend.)
I'm no expert, and this article is not written wholly or specifically about Spanish; however, it does seem to support Roger's claim, insofar as the present subjunctive is concerned. "Que" (the conjunction) is a flag that may qualify the clause that follows for the subjunctive (conjunctive) mood, as long as at least one of the other criteria are met. The author then goes on to write about the past (imperfect), the future (obsolete), and the past perfect subjunctive in Spanish.
Indefinite or non-existent antecedent
as I said at the risk of being beheaded by the grammar police. 
Hi:
You're right. Have you notice that the idea of doubt is out of these phrases? It's the idea of a doubt (incertainty) that carries the need of the subjunctive. When you master this idea, no need to learn a list (of tricks) even if they're really accurates.
