I don't play anoymore but this is what I would do if I was just starting out.

Level 1-60: At this level your main focus is just finding a guild you can use for the guild perks and meeting new people, you probably wont ever get to know the guild leader or officers. You will use them for perks and they will use you for the free cash and exp a guild gets from having members that are questing.

Somewhere in the starting area you will get spam-invites to join guilds. Check and make sure the guild is level 12 or higher then check to see if it has a bunch of low level people who also seem new to the game. If it has both of those things, join the guild and start making friends with people your level. It will be more fun this way because you will learn as you go with other people who are also new.

lev 60-100: Once you get to level 60+ consider leaving the first guild with a couple of those friends and joining a smaller more select guild. You probably keep bumping into the same people all the time when you are questing, so if you meet people who seem cool, make sure their guild is focused on the stuff you are interested in (pvp or pve) then ask to join their guild. A higher level guild is nice for the perks but it's not essential anymore because your main focus is joining a group of cool people. With a bit of luck you will get both.

Max level: At max level you will stay with that same guild because they are your wow friends now. You may eventually have to leave that guild if you get hardcore about raiding but it will be a LONG time before that's a problem. By then you wont need someone elses advice. You can do most of the game content (including raids) without a raiding guild so you might not ever need one.