Make sure it is seated well in the butt and that there are no burrs on the threads. Put the cue together and make sure the joint is tight. There should be no vibration or other sound except for the rubber stopper bouncing off the floor. If the joint is not perfectly tight, loosen it then reseat the ends again to make sure they are as flush as they can be. If the joint doesn't tighten well, forget about buying the stick, it ain't worth it.
Designs give a cue personality, but have no effect on playability.
As a matter of fact, they only affect payability. As an investment, make sure you get a well built cue, then you can focus on aesthetic appearance. Now a note about options. Many cues have various options which can be nice, but in general are not needed for regular play. Most average players find a comfortable weight and never need to adjust, so don't fall for that option.