Surrendering can be difficult. It's like telling someone not to think about a pink elephant. Don't think about a pink elephant. Are you not thinking about it yet? Of course you are! So how are you supposed to stop thinking about something you want? After all, it must be important to you if you want it, and if it's important to you, then you're thinking about it - probably regularly.
The irony is that although "what we think about, we bring about", what we stop thinking about, we also bring about. I have found that while thinking about things works, I am able to attract much quicker when i stop thinking. Why is there this dichotomy? it may be that thinking about something actually serves as a barrier to allowing the Universe to unfold in the way you need it. People do not realize that there is an extremely fine line between believing that something is yours and doubting that something will ever be yours.
Simply stated, when we place too much emphasis on thinking about our dream car for example, it shows insecurity and doubt that we'll receive it. If you really had your dream car you wouldn't be thinking about it anymore and would probably have moved on to wishing for something else.
The best way to "surrender" is to make your wish, then concentrate on other things, like another wish! It takes practice, especially when you may desperately need something and need it right away. But just keep wishing for other things, and keep moving on. Keep distracting yourself. Everytime a doubt enters your mind, remember all of the times your dreams did come true and renew your confidence that this one will manifest as well. But it will manifest when you surrender, and not one second sooner.