A common mistake is the use of ser or estar (to be) with nacer (to be born). This is redundent. Here are some examples of common mistakes and their correct form:

• Nací en 1988. - I was born in 1988. (correct)
  Estuve nacido en 1988. (incorrect)
• El bebé nacerá el lunes. - The baby will be born on Monday. (correct)
  El bebé será nacido el lunes. (incorrect)

Another common mistake occurs when one wants to express the idea of spending time. The Spanish verb gastar is used only when speaking about spending money. To speak about spending time you should use the verb pasar.

• Pasé un año en España. - I spent a year in Spain. (correct)
  Gasté un año en España. (incorrect)