As with all things, not every guild is for everyone. I belong to two guilds, both good people, both fairly welcoming. The smaller of the two guilds is more "open" to newcomers, but that means that because there are fewer members it is easier to get to know the other members.
The other group is bigger and a bit harder to fit into initially, but persistence does pay off. It also helps to volunteer to do something, but only if you can actually do it.
Tessagin: One member of the second group has been a member of that group for 20 years. She is a complainer, has envy issues, and listening to her you'd think she has the worst troubles in the entire world. If you meet someone like her at your first meeting, you will get the wrong impression of the guild. Note that this one person isn't a bad person once you get past all her armor, but it is tiring to spend much time with her.