Appearance should be 現象, 跡象, or 表面？
There’s a common idiom that expresses not judging people by their appearances:

人不可貌相

Oxford defines this as:


  don't judge by appearances


and gives the full phrase as its example sentence:


  人不可貌相, 海水不可斗量。
  As the sea cannot be measured with a bushel, so people cannot be judged by their appearances.


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The sentence you gave: 看事情不要看表面 is a good sentence and it concisely expresses what you want to say. 现象 can also mean appearance, for example ABC gives the sample sentence:


  光凭现象做判断
  guāng píng xiànxiàng zuò pànduàn
  judge according to appearance only


but phenomenon is still the most common usage.

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Another word you might want to know is: 长相, which explicitly refers to one’s physical appearance, looks and features.