I'm not going to break this down in detail explaining everything as you can learn what you need from reading the library. I'm just going to explain something very quickly.
Preparatory work to enable yourself to pray effectively
1. Know yourself to be spirit (Raja yoga / Arcane Teachings shit).
2. Practice the observation and control of thoughts (IIH step 1 shit).
3. Learn the qualities, attributes, etc. of God (Kybalion / theology shit).
How to pray
1. Decide which element you need the most. Practically speaking, you use all the elements every single time, but there will always be one you focus on more the others. In this case, we need to decide if we're going to focus on omnipotence, omniscience, omnipresence, or omnisentience.
2. Invoke, simply by focusing on the qualities of god you need to infuse into your working, and concentrate and enter the trance.
3. When you fulfill the requirements (see master formula of attainment) your will is done.
That simple. Takes a long ass time to get to this point, lots of meditation upon god, lots of cleansing out bullshit thoughts from your mind, lots of concentration upon qualities you need to balance out, and constant use and mindfulness of the hermetic laws (I shit you not, I think about the law of polarity and law of correspondence so fucking much, as well as thinking of the other 5 of the 7 laws).
If you're feeling weak and ineffective or doubtful, you have to focus hard on the omnipotence of God and invoke fire. If you feel deficient of knowledge, you need to focus on his omniscience, and that includes "the all in all" or "holographic principle" and such axioms as "from one; know all" – in this way you gain access to all knowledge on demand. If you feel deficient of desire or emotions, it's the omnisentience (this is a shit term for it but "all love", just don't think love has the usual meaning here) of God you need to focus on, as that will strengthen your emotions. As for omnipresence, that needs to be your main focus if you feel god has abandoned you or is not listening or some shit, you have to remember that God is the All in All, that God is ever present, he's fucking everywhere and everything and anything.