I have a few thoughts...
Your concept and thinking conceptually is a good thing.
The logo and car are not all that nice. The colors are not all that desirable. So right off the bat, you don't have a good foundation for laying this out... at best you are turd polishing. I tried my hand at laying something out and asked my muggle son (non-designer) what he thought, right off the bat he said replace the logo and car and it would look cool. (see images below)
What I tried to do was incorporate the colors from the car into the layout. Making the whole "brand" consistent... even if it's not all the pretty.
I've looked at your cut-vinyl work. You really need to spend the time looking at good work. Then try emulating it. Stop stretching, squeezing and pulling type, especially when one side of the sign is stretched differently than the other side. Lay off the cute display type unless you absolutely have to.
Most newbies not only have to learn how to design, they have to develop taste.
Now this is NOT a reflection on you or your work but it's been stewing in my head for a long time.
I went on a rant a while back:
http://www.signs101.com/forums/showthread.php?124229-Shop-logo-attempt&p=1236289#post1236289
I highly recommend you subscribing to Signcraft and
www.lynda.com
Don't learn the software... learn how to design and how the process works.
Post even your simple work here and many will help... I admire the guts it
took showing this.