Second, pay attention to your knife. This is more than a safety tip. Even if you can't make every carrot stick exactly the same size, make them as similar as possible. Practicing your knife skills is always part of cooking well. If you don't have the time or patience to cut perfect little cubes where diced veggies are called for, roughly chop the vegetables so that they are about the same size.
Texture can do a lot to make up for precision.
The Arizona Republic Stuffed shrimp salad is the elegantly simple eye-catch of the day. Third, remember that food is a natural thing. Every tomato is not the same size or color. Natural differences and inconsistencies actually add to the eye appeal of your food. Style is one thing, but too much of anything, even style, is intimidating.