Should I use a comma before “and” or “or”?

Whether it is correct to use a comma before a coordinating conjunction ("and", "but", "or", "nor", "for", "yet", "so") depends on the situation. There are three primary uses of conjunctions:

1. When a coordinating conjunction is used to connect two independent clauses, a comma is always used. Examples:
   
   • I hit my brother with a stick, and he cried.
   • The rain stopped, and the sun came out again.
   • Should I eat dinner, or should I play a game?
2. When a coordinating conjunction is used to connect a dependent clause, a comma is never used. This includes both of your given examples. Other examples:
   
   • The boy ran to his room and cried.
   • Frank is a healthy and active child.
   • Should I eat dinner or play a game?
3. When a coordinating conjunction is used to connect three or more items or clauses, a comma is optional (though I personally prefer to use one). Examples:
   
   • I bought cheese, crackers, and drinks at the store.
   • Should I eat dinner, play a game, or go to the store?
   
    Here's a good guide: http://www.grammarbook.com/punctuation/commas.asp
   And some examples:
   
4. I fell over and hurt my knee.
5. I fell over, hurt my knee , and got stitches.
6. I like the colors red and blue.
7. I like the colors red, blue , and purple.
8. You can buy an apple, a pear , or an orange.
9. I can go or stay - which would you prefer?

When used in a list, and and or never take a comma when the list has two items; when it has more, it is generally a good idea to use the comma.
When used as a conjunction it is generally a good idea to use the comma (unless the phrases are very short).

Source:
http://english.stackexchange.com/questions/30516/should-i-use-a-comma-before-and-or-or