Always take a hostess gift when invited to someone's home for a party or dinner.

My mother never taught me this either.  However, when we went to someone's house, it was usually family, or it was to their friend's where they rotated hosting the card party, and nobody took a gift because they did this each month, and they would always be bringing gifts to each other.  But my oldest daughter was just invited to her sorority sister's new house for a pot luck dinner.  Although she was bringing a covered dish (which is usually the "gift" to the hostess), I encouraged her to bring a small "consumable" item.  This doesn't cost much, and it shows the hostess that your really appreciate her hospitality.  A bottle of wine, a candle, a lotion, etc. all work nicely as a hostess gift.  I invited a friend over for dinner who doesn't drink, and she brought over a specialty bottle of extra virgin olive oil.  What a nice, thoughtful gift that I was able to use and I thought of her each time I used it!  And if it was a really nice event, and the hostess worked hard to put it together, a hand written thank you note sent afterwards is always a welcome and thoughtful gesture.  And as you raise children, teach them the value of the written thank you note.  Are there exceptions to this rule?  Yes, if you are invited to a party where you are expected to purchase something (Pampered Chef, Tupperware, Party Lights, Stella and Dot, etc.) you are not expected to bring a gift, or if you are going for a shower, where you are bringing a gift for the honoree, then you are not expected to bring a gift for the hostess.