"Blog what you love" - that's definitely the first step. But also have a clear goal as to what it is you want to achieve. It's quite alright if you're doing it for money, even Amit Agarwal started labnol to make money and he wouldn't be spending anywhere as much time or effort on his blog if it wasn't making him money.
Whatever you do, just don't half-ass it. I'm not saying that in a bad way, mind you. What I mean is - it takes a LOT of research, time and effort to put out a really noteworthy product. Anyone can open up a blogspot blog (like Amit did), but only a few can rise to the top (like Amit did). It's not just about content - its about GREAT content. And that's just the beginning...there's also design, usability, connectivity.....your readers must really and truly want to come back after seeing your blog the first time.
You have to be willing to put in the time and effort to get that 'WOW!' response from your readers. There's no substitute for hard work when it comes to making your blog(s) a true success.
Few things to keep in mind -
1) Don't stay long on blogspot. It just screams 'SPAM BLOG!'. Move to wordpress, get your own hosting, and design a killer look - something different, edgy, attractive. Remember that first impressions count for a lot when it comes to repeat visitors.
2) Be original - this is absolutely crucial. You have to give your readers a mix of something they can't find elsewhere, or at least not in a lot of places.
3) Study what works - you don't have to reinvent the wheel here. When you decide on a niche, start studying the blogs that are the big players in that niche. For tech, it would be blogs like techcrunch, gigaom, labnol etc - make a list and figure out why they work (again - do NOT copy any content from anyone!)
4) Study what doesn't work - by the same token, you should also know what doesn't work and avoid it. There are plenty of failure stories out there - learn from them.
5) SEO - search engine optimization is vital for your blog's growth. Spend some time going through renowned 'blogging' blogs like problogger, chris garrett, copyblogger, daily blog tips etc to get comfortable with SEO
6) Traffic - SEO is not the only way to get traffic. For example, social media plays a HUGE role in drawing traffic. Again, spend some time reading up on trafficking tips from the 'blogging' blogs.
7) Monetization - don't be fooled. Adsense is merely the tip of the iceberg. The top bloggers (like Amit) don't rely solely on adsense to make their hundreds of thousands. The true money lies deeper - private advertising, affiliates etc. Again, do your reading.
8) Stay up to date - Keep a steady reading list and make sure you keep up with all the latest developments. Not just in your niche, but on the blogosphere in general. Here's a good place to get started on your reading list - http://www.labnol.org/websites/
9) Keep tweaking - your content, look, design, monetization strategy - there's always something that can be done to push it a bit further. Always keep working on improving your blog.
10) And Finally - Language! - As an Indian, everytime I come across a desi-owned blog that's poorly written, I grimace inwardly. The fact of the matter is that the whole world will see your blog and bad writing speaks volumes about the worth of a blog. So make sure your english is impeccable. It doesn't have to be prose on a shakespearean level or anything. As long as there aren't any grammatical or spelling errors, you're off to a good start.
(The secret to writing well - reading a lot! Read all the major publications and blogs as much as you can. See how they do it and learn.)
That's a rough blueprint to get you started. Honestly, start with reading the 'blogging' blogs and you will begin to get an idea of what works and what doesn't.
Good Luck!!
Hope to see you become famous in the Blogosphere :)
Knight