1. About topic, I'll do a little bit of research before I write. Have you heard about "keyword research"? There are free tools fit for keyword research. Not only for blog but for any kind of writings, if Internet is involved, I do keyword research first. For example, for this article, I took a little bit of time to find what kind of keyword people are using when they want to look for information about how to make money from blog. And I found people are using "make money blogging." This keyword research has two fold benefit. One is that it helps you fine what kind of topic people want to read. The other is that by using these keyword you'll have better chance to be positioned high in search engine result page.
2. About question 2, I'm thinking about what monetization method I'm going to use. Am I going to introduce an affiliate program, a book or place Adsense?
3. The purpose of asking question 3 was to emphasize word "PREsell". In blogging, though you want to sell something or want your visitor to click links, don't rush it.
What do you do if you see a blogger is doing nothing but a sales pitch. You leave him once and for all, don't you? So PREsell is key of how to write.It is something like creating a worm mind to your suggestion.
If you want to make money from your blog, start writing it only after you know what keyword is related your topic and what kind of monetization you can apply. This can make a huge difference.
If you want to know about how to do a keyword research, you may want to read this blog, Traffic to Blog: Keyword Research.
To sum up, a blog that can make more money is;
1. a blog talking about topic people want to read and this can be found by keyword research
2. a blog that uses the keyword in post so that search engine can easily pick up
3. a blog that PREsells product by creating warm mood.

How to know supply of keyword?

• For this end, you don't need any other tools. Just go to Google, Yahoo or whatever search engine you like and type car in search box.
• Look upper right bar of search result page and you can find something like "Results 1 - 10 of about 301,000,000 for ''car". The number '301,000,000' is approximated number of supply. For sure, not all of them are blog, but realize that if you talk about car you're just 1 out of 301,000,000. This means that you may not pick up "car" as your keyword and choose other topic if you want many visitors to find your blog from search engine. This is why you need to save above demand table somewhere.
• Now that you know topic "car" is too competitive, next thing you can do is to find number of supply for other keywords from table you saved. Continue this step until you find less competitive keywords.

You may choose several keywords and use them in your blog. But remember that if you post a short blog, it's better to focus on only one keyword. If it's long, you may choose primary and secondary keyword.

To sum up,

• Use Search It to find reasonable demand of keyword related to your blog.
• Check number of supply from a search engine, for example, Google.
• Choose keywords that have high demand and low supply.
• Finally use that keyword in your blog repeatedly with frequency of a bit more than your high school English teacher would tell you.