Mark’s answered a lot, but to clarify and reinforce a few points:
Nation changes: Frequently. My current IC boss started in Varushka, spent much of his IC life in the League, and is now in Dawn. It’s a similar level of hassle to changing national citizenship in the real world (but if everyone spoke the same language); a certain amount of formality and ceremony, but common.
Glasses: I advise picking a set of glasses (if you have the option) which are fairly close fitting and low-profile. Something with plain, metallic or dark frames. A spare pair is a must. I have had one LARP event where I lost my glasses halfway through, would not reccomend…
Dawnish Houses: Hello, I’m the Dawnish mod… 
Knight Errant is a great way to jump into Dawn, because it means you play someone expected to be going around, asking questions, introducing yourself, and getting offered quests. And everyone wants to recruit you.
What is usually done is to pop up at Empire with a Knight Errant costume* and visit the various Houses asking about them. This is easy, gamers LOVE talking about their characters and organisations.
You’d be wanting to join a House, led by an Earl, who would give you a Test of Mettle to complete. This would have you start as Yeofolk Moonandstars, be Sir MoonandStars of House X when on the Test, and finish as Lady (or Lord, or whatever) MoonandStars X when complete.
How this works in play is you’ll be wandering around, talk to various folks, chat to various Earls and see what sort of Houses take your fancy. You can then ask for a Test of Mettle to join that House, from the Earl. They will then set you a quest… (many examples available on request). As a Knight Errant, you aren’t expected to be automatically loyal to that House: you don’t need to camp with them, fight alongside them, or whatever. But most folk generally do, so you’ll see several Houses with their Nobles, their Yeofolk, and a couple of Knights Errant associated.
It’s possible to fail a Test, or give up on it, and perhaps beg for a different one from a different House. It’s possible to be offered a Test by an impressed Earl. It’s even theoretically possible for them to offer adoption on the spot, but that’d take something extreme…
[Did you just kill that hydra by yourself?
I did milord, what of it…
I want to you join my House!
Are you going to set me a Test of Mettle?
Well it was going to be slay some great monstrous beast single-handed, so I think we’ll assume you’ve passed…]
(a band is slightly different, depending on it’s purpose)
*This is a pretty simple costume requiring a yellow sun symbol on blue. Many patterns and hints on these are available, they can be elaborate or basic, and you may be able to purchase them from LARPers if you don’t want to make one yourself.
Advice for New Players:
Erm, general advice we have by the bucketload, here and on the facebook pages…
https://www.facebook.com/groups/playersupport
Have a browse, or ask us some more specific things 