Steps To Being a Webmaster

1. Get a solid grounding in HTML. Plain old HTML. Whatever the most recent version is. General stuff - basic HTML, tables. Learn enough CSS that you can cut+paste it, if not write it yourself. Check out www.w3c.org - they spec'ed it, they have great reference stuff for it. A development tool like Dreamweaver can be useful, because you can always get your feet wet in the HTML, while still getting to see what it looks like, and playing around with a GUI. Frontpage is more widely available, but it's also less easy to see the code in Frontpage, so I prefer Dreamweaver.
2. Learn a server-side scripting language. PHP is my favorite, but PERL is also a good choice. Make sure you understand how to use a database with your scripting language of choice, because most of what you'll be writing will be database code - forums, login code, ad servers, news, lookup stuff... it's all best done with databases.
3. Finally, you can learn JavaScript, DHTML, Flash all that. It's candy, and it doesn't always work, certainly not always well, and older/less complex browsers (lynx, for instance) won't use it at all. Remember the golden rule of web site development: Make it work for the lowest common denominator.

• The Web. It's not a book, I know, but it has some really good resources, especially for reference. www.php.net has a complete reference to the PHP language on the site, just as good as any book, and www.w3c.org has the same for HTML, complete with all the most recent updates.
• Anything by O'Reilly. They have good books. that's all there is to it. Read a review or two, first!

My additions then

• Knowing HTML is not enough. Knowing what seperates valid HTML from invalid HTML is important. All the development tools available allow you to write HTML which is invalid. This trips up differing versions of differing browsers, some of which you may not check with. Use the W3C validator.
• Know what a DTD is, and use it.
• Learn CSS so you can write it. Learn what browsers support each part of CSS. Have asprin handy when you do this. Cutting and pasting it is not enough.
• Have as many different versions of as many different browsers on your machine. Check public facing web sites with them all. Know each browsers kinks.
• Know your version numbers, especially for Javascript.
• Test your site on varying connection speeds. Too many people think their site runs great on their local machine, and end up having pages that are 250k or greater.
• Not everyone has your sight. If you can, build your site with support for braille browsers, for speech browsers. Don't use absolute font sizes. Use percentages wherever possible.
• Never rely on client side capabilities. Using javascript for form validation is not a good idea.
• And personally I'd say learn server side after you have mastered the client side stuff, there is no point in doing funky stuff server side when you don't know how to display the results properly. Be it PHP, or ASP it doesn't matter.
• Always remember View Source. If someone else has done it, you can see how they did it. Borrow.

A Webmaster has to manage a whole website, not necessarily program it from the bottom-up. The webmaster should know each and every thing about his servers on which the site is hosted. Sharp knowledge of HTML, CSS, JavaScript, and server-side scripts is required so that he can make quick changes to the website himself. He should know the ins- and outs- of disaster management when something goes wrong with the server/site.

A webmaster should also be savvy with security discussions, as he should know exactly when and how his site is being attacked upon, if somehow.