In terms of general Web strategies:

http://news.ycombinator.com/item?id=341138

http://news.ycombinator.com/item?id=351709

But here are some tips specific to niche blogs. I run a niche blog that has 17,000 subscribers and am in the process of building up others, so I have a few tips (but I am by no means an authority on this!):

- TWITTER! Use search.twitter.com to find people talking about your topic and talk to them. Follow them, get them to your site. Twitter about your topic. Use TwitterFeed to stream the titles / links to your blog posts into your Twitter feed.

- Sometimes niches are interesting to broader audiences. On HN you see stories relating to the Ruby programming language (or Rails) all the time - these are pretty niche topics but with some general appeal to hackers / programmers.

- Find the other blogs. Comment on them wisely and try to build up relationships. Find areas where you can complement what others are doing rather than just copying them. For example, let's say your blog is specifically about flash photography. You could get interest to your articles from general digital photography sites! If you're going to be niche, find the blogs that are one thicker branch further down the tree.

- Blog carnivals ( http://en.wikipedia.org/wiki/Blog_Carnival )

- Get "outsiders" interested in your niche! I wasn't really all that interested in typography or logo design, but ILoveTypography ( http://ilovetypography.com/ ) and Logo Design Love ( http://www.logodesignlove.com/ ) hooked me with their awesome designs and modern, friendly approaches.

- Advertise with Google Adwords. You can target very precisely this way.

- Advertise on complementary blogs.

- Look for Facebook groups on your niche. If you find some (and there are millions), you have a whole index of people who might want to subscribe to your blog.

- Try to get included on to "planet" sites for your general topic area (e.g. for the Ruby world - http://www.planetrubyonrails.com/ ) and on to sites like Alltop.com.

- Guest post on complementary blogs.

- Engage with whatever audience you build up over time. These people need to be your advocates! If they blog, they should be mentioning you from time to time, assuming your content is good.

- Editorial mentions in magazines relating to your niche. Many smaller magazines like to mention Web sites that could be useful to their readers. You will probably need a bit of a track record first though unless you're really unique.

- Start your own Digg / Reddit-a-like on your topic area if one doesn't exist. If one does, use it!

- Start a podcast on your niche. Interview people. Start with lesser known people and work your way up until you have a good track record. Heck, even just interviewing people by e-mail and putting it on your site is a start. It's all about adding a human element.

- Have a Google Alert on keywords relating to your niche. Make sure you know all the news and make sure you get commenting on any blog that even mentions your niche in some way. You need to become known.

- Subscribe to both ProBlogger ( http://problogger.net/ ) and CopyBlogger ( http://www.copyblogger.com/ ). If you haven't visited them before, exhaustively read their archives. They are PACKED with tips on how to promote niche blogs.

It is important to remember that the techniques you use should be based upon your target demographic. If it's bridge playing retirees, then Twitter and Facebook probably aren't going to cut it.. whereupon I'd look at editorial mentions in magazines, etc.

Added: Check this out too: http://jessicaknows.com/2008/11/15-days-of-marketing-day-one...