The 2 most common blogs would be wordpress and blogger. Topics could be anything. I think personal blogs out number any other topic. Blogger is easy to set up so is free wordpress blog.
If you need some tutorials on how to set up a blog, just click my "free wordpress video tutorials" signature below. These videos will show you step by step on how to use and install wordpress. Good luck!
1. get a domain 2. make a unique skin 3. put QUALITY unique content. If you plan on being another worthless copy-paste blog, save your time and do something else. Chose a topic you know a lot about and put some good content there 4. install hacks (modifications) 5. start promoting 6. write articles frequently and regularly. Promote and keep up the content. Other tips: 1. open comments .. it's a nice thing to also have feed-back 2 disable the rel nofollow on external links (wordpress has it's by default, there's a hack for this) 3. put some "top commentators" plugin on the site .. makes people comment more 4. comment on other blogs and write USEFUL stuff. 5. Don't spam and don't let others spam. WORK A LOT and you'll make it