I still consider myself a newbie and we've been playing the game for about 4-5 years now. My big advice is to read, read, and read some more. Try to understand everything about the card you are applying for, what you will get out of it, and exactly how you plan to use it. This helps a lot in the beginning.
And keep in mind that you win some, you lose some. (so don't get too frustrated - keep the risk level at one you feel comfortable with. Always consider worst case scenarios)
I remember one of my first cards, I read and read and read some more. And even then, I got burned at redemption when it didn't process the way I had planned. In the long run, it was OK as I was able to use the leftover points for something else but it was a little frustrating in the beginning. Now I know how to roll with the punches :)
Have fun! We started out small and now apply for 5-10 cards a year. It's a really fun game (but does take some time). In recent months, we haven't had as much time and energy for it so we have scaled back some.