Well, most of us have gotten the new customization update and after playing with the thing for a couple hours, I have a couple tips of advice:

• On the far left is a list of all the applied decals. They are arranged by layer, so if you want to put decals on top of each other, the higher decals have priority. Essentially the decals are rendered from the bottom of the list to the top of the list.
• Don't be afraid to put decals on top of each other or at least overlapping. This is necessary if you are to receive nice flowing trim. For example, I put a smaller black circle inside a white circle and created a donut on the top of my Lambo:

• Red and black look good together

• Try to follow the cars natural lines instead of pasting decals on the car. This will help them flow better.
• The amount a car's ride height can be raised or lowered depends on the car and whether it's the front or the back.
• If you want a low rider, try a '69 Dodge Charger. She'll go down 5.94 inches on either end.

• The mirror button on the top bar is great for symmetry. The Apply Through button will apply the decal all around the car (essentially. I'm still not quite understanding this one.)
• Use the camera button to center your decals on different places of the car.
• You can move the decal by touching and dragging, rather than rotating your car.
• Use the check button on a decal HUD to confirm an icon. Don't be afraid to hit, you can remove for free and reapply for free whenever you want!
• Use the circle button on the right on a decal HUD to make the icon bigger or smaller and rotate it 360 degrees.
• To achieve some nice complex patterns, take a rather irregular icon (e.g. not a square, but the racing flag with flames coming out the back say), mirror it, then bring it to the center of the car. The pattern itself will always be dead center and they can look really cool:

• Be creative. There are a nearly infinite amount of different ways to combine decals.
• Although you have 50 decal slots, you really don't need that many. Otherwise, your car will look very crowded.
• You have the same decals to choose from every time and you have to buy them per car. And you need to pay gold if you want to unlock decals and directly visualize them. So figure out exactly what you want before you waste gold by buying decal packs.
• All other customization options, you can at least visualize before paying up.
• Dropping ride height on the right car can look pretty cool. The above Porche's ride height is as low as it goes.
• Putting "EAT MY DUST" on your back bumper is cool ^_^

• For photo mode, the top right button changes whether the background props are blurred or not. Activating this brings your car to the center of the focus and is generally a way to improve a photo shot.

• Advertise MRR. From your rear bumper.

I think that's all I can think of! If you have some of your own, post 'em in the comments and I can add them ;)