You should not feel gratitude for something you don't actually have btw.
The proper feeling you must have is gratitude that the thing you want to manifest is already secured.
Like, lets say you want a pair of gloves. Merely feeling grateful for a pair of gloves when you don't have it won't work. However, if I told you I'm going to go out and buy you a pair of gloves and gave you my assurances you'd have some gloves soon, the feeling you'd get right then is the right feeling.
You must go into a deep gnostic trance and reach a place where you feel that you have seeded into the akashic plane (plane of causal-energy/desire) the cause of the manifestation of the whatever it is you want.
The more intense you make this, the faster and more forcefully whatever it will manifest, and it may even manifest instantly.
Some other variables are:
There is a formula that applies here: The probability of the thing manifesting, how specific or general the request/intention is, the intensity of the desire forced into the askahic sphere to seed the cause of the manifestation.
That which is less probable to happen takes extra bruteforce to manifest. That which is very general in its nature may manifest in many different ways and so is easier to manifest (e.g. the death of a person is actually easier to manifest than removing a mole from them, because there are way more ways a person can die, than a mole can be removed), and the very most intense desires when coupled with Imagination and Will can manifest extremely improbable events.
Montalk has a good article on this: http://montalk.net/notes/reality-creation-redux