1.Create a blog on topic you really interested in, or on topic you have good knowledge. Then start add articles on your blog. Update your blog articles every few days.
2.Add adsense to your blog.
You can edit your wordpress theme files to add adsense code directly ,ff you know something about php/html code.

If you have no idea about how to insert adsense code, you can just use Easy-Adsense plugin. It is recommended by Google Adsense officially nowadays. Easy-Adsense is very easy to use and has the option to select show only three ads per page.Easy-Adsense has author links under the adds but you can remove it by set the option .
There are many other plugins such as: mightyadsense, Adsense manager.all very easy to use.

3.Get traffic to your blog.
Subbmit you blog to seach engines, directories, rss, digg etc to get traffic.

Remember ‘content is the king’. It’s important to have unique content on your blog to earn more.

It’s so simple, you see. Now just start creating your blog and making money . Good Luck.

Basic Tips:

AdSense Tip #1: adsense placement:

Place the ad around the main content of your website.

Place ads near a image/images will make more visitors to see your adsense thus improve your CTR.

AdSense Tip 2: adsense colors

Try to select ad color “melt in “or “stand out ” with your pages.

change your ad color frequently will improve the CTR from your old vistors.

Add variety and freshness to your ads by rotating between several color palettes.

How to do it?:choose the Use multiple palettes option when generating your ad code during the Choose Ad Format and Colors step in the ad code setup, then hold down the Control or Command key and select up to four color palettes.

google_color_border = ["c8ccc8″,"ffffff","ffffff","000000″];
google_color_link = ["0000ff","0000ff","ffff00″,"63b4cd"];
google_color_bg = ["f0f0f0″,"f0f0f0″,"ffffff","ef6c6c"];
google_color_url = ["666666″,"666666″,"000000″,"000000″];
google_color_text = ["999999″,"000000″,"000000″,"000000″];

Rotate your adsense ads and other ads will improve your adsense earning
and total earning.

AdSense Tip 3: Use section targeting

Sometimes you may can’t get targeted adsense ads. Try use section targeting to emphasize some content in your page. Place following code where you want to emphasize on your pages.
<!- google_ad_section_start ->
Content you want to emphasize.
<!- google_ad_section_end ->

If you want some content to be ignored, use
<!- google_ad_section_start(weight=ignore) ->

Ralated info:

https://www.google.com/support/adsense/bin/static.py?page=tips.html#17954

Text Ads
Horizontal:
Leaderboard (728 x 90)
Banner (468 x 60)
Half Banner (234×60)

Vertical:
Skyscraper (120×600)
Wide Skyscraper (160×600)
Vertical Banner (120 x 240)

Square
Button (125×125)
Small Rectangle (180×150)
Square (250 x 250)
Medium Rectangle (300 x 250)
Large Rectangle (336×280)

Image ads
Leaderboard (728 x 90)
Banner (468 x 60)
Skyscraper (120×600)
Wide Skyscraper (160×600)
Medium Rectangle (300 x 250)
Large Rectangle (336 x 280)
Square (250 x 250)

Link Units
(120×90) (120×90_4)
(160×90) (160×90_4)
(180×90) (180×90_4)
(200×90) (200×90_4)
(468×15) (468×15_4)
(728×15) (728×15_4)

Adsense channel

google_ad_channel =”";

Alternative color

google_alternate_color = “0000FF”;

Alternative ads

google_alternate_ad_url = “http://www.toplistweb.com/ads.htm”;

Adsense on a Framed page

google_page_url = document.location;

Adsense ads color rotate

google_color_border = ["c8ccc8″,"ffffff","ffffff","000000″];
google_color_link = ["0000ff","0000ff","ffff00″,"63b4cd"];
google_color_bg = ["f0f0f0″,"f0f0f0″,"ffffff","ef6c6c"];
google_color_url = ["666666″,"666666″,"000000″,"000000″];
google_color_text = ["999999″,"000000″,"000000″,"000000″];

Adsense section targeting

<!- google_ad_section_start ->
Content you want to emphasize.
<!- google_ad_section_end ->

If you want some content to be ignored, use
<!- google_ad_section_start(weight=ignore) ->