Everyone needs to be smart about choosing online passwords. Its important to not use the same password for everything. Also your passwords should be long and include letters, numbers, and even symbols. Making a secure password may require you to write it down somewhere which is fine just make sure to keep it somewhere private. Don't use passwords that are easy to remember because someone else may be able to guess them.
Many websites or advertisements are dedicated to scamming online shoppers and users. They can range anywhere from an ad suggesting that you have been selected as a winner to a sketchy website selling products way below retail price. One good thing to keep in mind is that if it sounds too good to be true it probably is.
Privacy is very important online. Once something is posted or uploaded it stays on the internet forever, even if it is deleted. This is because everything online is saved to one of many databases which can be used to find anything that has ever gone through the internet. For this reason never post or say anything online that you wouldn't in person.
User agreements are most likely the least read documents out there. Being usually more than a page of small text and containing uncommon vocabulary, everyone has at some point skipped over a user agreement.