It really depends on the guild. Different guilds have different policies as far as adding new members.
Basically, your best bet as far as being in a guild is to get to know people in the community and give people time to get to know you. Eventually at some point if you feel you've gotten to know folks well enough that you think you have something positive to offer someones guild, tell people you're interested in being in a guild. Let em' know why you think you'd make a great addition to their community.
Or, start your own guild. I did. It's really not that hard. You just need to find a bunch of like minded individuals who share a few common interests who are able to play well with others. I ended up having so many people interested in my casual-friendly gaming guild that we eventually had to close registrations (kinda hard to get to know your fellow guildies well enough that you can honestly say you trust them, when there are over sixty of em' lol). Just don't be afraid of letting people help (and make sure you make one or two people you really know well, trust and really get along with officers and delegate, delegate, delegate!)
The world is full of Kings and Queens
Who blind your eyes then steal your dreams
...it's Heaven and Hell, oh well