Before going to attending the first open house, should well researched on that house like its area, price of other houses in that area etc. As well as create a list of expectation home as per your need will help to take decision for the first home and also go good to ask questions based on the house as per your expectation.
If you are in need of financing that would be your first priority. Getting preapproved will allow you to make offers quickly if you are interested. If you are paying cash then no need. I also recommend interviewing an agent to assist you on your home search. They can tailor a search to your needs and even take you on a tour of several properties in one day. Open houses are good to get a feel for a home or neighborhood however Realtors make the magic happen for you. I recommend you call Jillian Batchelor at 702-595-8036... She is one of the best in Las Vegas, NV