1. When you're shopping online you have to be sure you are aware who you're buying from. If you're buying on an online auction site, only buy from people that have positive feedback. On other sites look to see if they are a reputable company by looking for reviews on them online.
2. Make sure to read all the information about any product you are considering purchasing. Just looking at a picture online can be deceiving sometimes. It will make a product look bigger or smaller than. Make sure to browse the description so that you know exactly what you really are purchasing.
3. Make sure that you're entering your payment details on a safe and secure site. Look for "https://" inside the URL of the site that you're trying to buy something from. If you don't see that or no symbol of any website security, then it's probably a good idea not to trust those people together with your account information.
4. Look for the right times to shop online. Often the stores that you frequent will have online sales that follow a time pattern. Many, for instance, schedule sales for the beginning of the month or at the end. When you see there's a pattern, hold off on buying anything until the upcoming sales period begins.
5. Be skeptical of overdoing it. It is much easier to overspend if you are shopping online. You begin to rationalize that you can spend more money for those shoes because you saved money on gas and the food you would have gotten if you went to the mall, for example. Give yourself a limit and follow it.