First thing's first.
You don't need to sign up for a domain or anything major like that. You can sign up for free sites that can host your blog such as Blogspot, Wordpress, or Multiply. There are also sites like LookBook.nu and Chictopia.com for fashion bloggers who also want to interact with a community.
A picture is worth a thousand words.
If you're starting a fashion blog about your fashion, then you'll need a camera (a point-and-shoot or camera phone will do unless you want to be all professional about it and whip out a DSLR). Have someone take your picture or activate the self-timer on your camera. You can also take your picture with a mirror.
If you'll be blogging about fashion trends, then you'll just need to get pictures from magazines or websites. Just make sure to properly credit these pictures when you'll post them on your blog.
Although you might be using material (like pictures from the runway or from a designer's lookbook) that someone else will be blogging about, your opinion about it will probably be different. People will start following your blog because of your insights so blog what you know and your fans will start flocking.
You'll get by with a little help from your friends.
If you're new to fashion blogging, it'll help to do a bit of networking. Link to your favorite fashion blogs, comment on their posts, and invite your friends to visit your blog. The more active you are online, more people will read your blog.
No to cyber bashing.
Don't get into flame wars with your readers or the subjects you post about. If you have a negative comment about something, don't expect everyone to agree with you. (If you don't like a certain style, it doesn't mean everyone else doesn't) Don't get catty when someone comments about your style. You can't please everyone. If the comments bother you so much, screen them so that you only post those that you like.