Mail your invitations anywhere between 6 and 12 weeks prior to your RSVP date. 8 weeks (2 months) is always a safe round number allowing your guests ample time to plan and respond.
Get yourself an Emily Post Wedding Etiquette book. Know and understand the proper etiquette in how to address, assemble, what to include, and more importantly, what NOT to do.
We live in a world where everything is all about digital, convenience and no-fuss. But remember, your wedding and how you behave during the process will say a lot about you. Be mindful and courteous. Never assume what someone will or will not do. Never mail more invitations than seats. Never include registries. And above all, remember: While it is "your" day, it's really more about how you treat your guests and how you make them feel.