Appearance is extremely important to Spaniards. They dress elegantly, even for casual occasions.
Dress conservatively. Avoid bright or flashy colors.
Shoes are the most important element of dress. Shabby looking shoes can ruin a very nice outfit.
For business, men should wear jackets and ties, even in warm weather. If the senior person takes his/her jacket off during a meeting, you may do so, too.
Women should wear dresses, blouses and skirts.