Here's the simple trick. After saying your affirmation add the following phrase ... "My subconscious mind says Yes, O.k , I Agree, Let's Do It"
For example. I am getting better and better at saving money
"My subconscious mind says Yes, O.K, I Agree, Let's Do It"
That's it! Try for 21 days (the time it takes to form a new habit) and watch how it makes your goals achievable faster, easier and more efficient.
I'm not sure why it works, all I know is it does. Give it a try. For a simple tip for doing affirmations successfully see this Warrior Post. Make sure you're following these steps or the phrase just mentioned won't work as efficiently.