Joining collector clubs or societies is a great way to connect with even more people who share your interest and passion for collecting whatever areas you like best. For general collecting of stamps there is the American Philatelic Society. For those who collect first flight covers the best group is the American Air Mail Society and you can join by going to their website at
http://www.americanairmailsociety.org . There are also societies for first day cover collectors, navy ship cover collectors, military censored mail collectors, etc. etc. etc. Most of them sell good catalogs of material in their area of interest and if one is going to collect something, spending some money up front to learn about the material, what to look for, how to identify things, and the values and so on is a really smart investment.