Edit: June 17th, 2008: What the fuck happened to the formatting? Fixed.
...because guild applicants and guild officers don't always see eye-to-eye in terms of membership application and evaluation procedures. Raiding guilds take themselves very seriously, perhaps too much so in many cases. If you don't like that, you don't have to apply.
1. Follow directions!
Some guilds have really specific application procedures, read the forum stickies, etc. Here's a protip: How well you follow read and follow directions is often a part of our prospective member evaluation procedure. Also, some guilds like long apps, some like short apps...it really varies.
2. Read the guild documentation
This includes, the guild guidelines, the charter, DKP rules, anything stickied, etc. When you apply to a guild it is assumed that you have read all guild information provided and have agreed to all terms. If you have a question regarding loot rules, guild policies, or whatever, ask an officer for clarification.
3. Read the schedule and raid times
What time zone is this guild in? What times and days do they raid? Can you consistently make all guild events on time and for the entire duration? Can you make a long term commitment? No one likes new members who vanish a week after being ginvited due to real life situations that they "forgot" to mention.
4. Learn about the guild's culture before applying
Some guilds are prudish, some spout sex jokes every 5 seconds, some are composed of adults, some are composed of 12 year olds, some are casual, some are not. Guild officers not only want good decent, but people who will mesh well with preexisting players. Hint hint hint: a guild isn't going to get up and change just because dick jokes make you feel uncomfortable. Deal with it or don't apply.
5. Don't apply or trial for multiple guilds at the same time
I know it may seem more efficient, but this offends many guilds...who will instantly deny you any chance of membership for applying on another site. Remember: Guilds are looking for members who are committed to their guild, not every guild on the server.
6. Don't schedule multiple trials
Basically the same answer as above. I've had people schedule multiple trial runs with multiple guilds at the exact same time and wonder why their application was denied. WTF?
7. Don't make a "copy and paste application"
Most guild sites have a specific form that they wish to be filled out. Use that format, not your own. There are two reasons why: 1. It shows that you can to some extent read and follow instructions, 2. Having all applications in a standard format makes it easier for the officers to read.
8. Spell check
Use properly punctuated English, spell check and make sure that your application isn't one huge block of text. Most guild officers have an instant bias against applications that they are unable to read. If you can't give me the time of day to write a readable application, I'm not likely to give you the time of day for a trial. (By extension, please please don't write Walls of Text. Paragraph = friend).
9. Don't lie
Why do people outright LIE on applications? We can see your gear and spec in the armory, we can determine approximately how much experience you have in certain instances by looking at your rep, and we can also find your REAL guild history as well as interview your former GMs. Honesty, even from people with colorful guild histories, is appreciated.
10. Don't omit information
If there is a question that you can't answer or wish to keep private, just say so. Omitting important information looks suspicious.