Dress code is dependent on individual establishments, some casual, others keen on sophistication.  Places of worship specifically do require you to dress modestly while visiting.
 
As you roam around, you will organically get a sense of what works best.

Bad language, loud behavior, and encroaching on other people’s boundaries are considered disrespectful. Respectful public decorum is always advised.

Using polite words in Arabic (e.g., Ahlan for Hi, Shokran for Thanks) is encouraged and viewed as a gesture of endearment.

Certain shops close briefly during prayer times to allow time for worship.

During the holy month of Ramadan, the rhythm of the country changes into a mellow, spiritual one that allows savoring the revered month. Learn more about how to participate in Ramadan while in Saudi, whether you are visiting Jeddah or Riyadh.

The sale, purchase, and consumption of alcohol and drugs is illegal in Saudi Arabia.