One of the key tenets of ThetaHealing is being able to manifest. EVERYONE can manifest, but how effectively and WHAT they manifest varies a lot.
In "The Secret", Rhonda Byrne explains that whatever we put out, (or put another way) whatever we focus on, THAT'S what you'll attract. If you keep moaning about how miserable a day it is, you're going to have a miserable day. However if you choose to focus on the good parts, you'll notice and attract more of the good (even if there is still not-so-good stuff going on too). "The Secret" is just another way of looking at manifesting
First off, you probably want to look at any worthiness issues you may have. If you don't feel you're worthy of attaining something it probably isn't going to happen.
Then you need to decide what it is that you actually want - and that's not as easy as you might think. Explore what would happen if you got it. An example I use sometimes is if you want horses, who's going to look after them if you go on holiday? Think about what you want, what you need to make it happen, whether you need help, etc.