Let's start with Adsense!
With Adsense, you are paid for every click made to advertisements featured throughout your blog. It's free to join as an Adsense advertiser, and you are able to generate code which you simply copy and paste into your blog pages which will feature advertising boxes from various merchants.
To sign up, visit www.Google.com/adsense and create your account, if you don't already have one. Once you have it all setup, you will be able to customize the size and color scheme of your Adsense advertising boxes so that it blends well with your existing blog's theme.
This is an easy way to start making money with your blog even with little traffic, because rather than selling directly to your target audience, you are simply making money each time a visitor clicks on your ads, costing them nothing in the process. You earn money even if they never purchase anything from these external websites.
You can also create campaigns within your Adsense account so you can have a number of different advertisements across a network of blogs, which will give you the ability to determine what advertisements are converting and working well, and which ones may need to be tweaked in order to better perform.
You will also want to create individual channels for each blog you plan to feature Adsense on, in order to determine which campaigns are working well, and track the CTR of each advertisement.
If you find that a particular ad isn't performing well, you can choose to change the placement, color scheme or size of the ad, as well as the general channel so that your advertisements are highly targeted to your audience. Just remember to really call attention to those ads by choosing a theme like Socrates.
Side Note: From personal experience, larger square ad boxes convert better, with the colors modified to blend well with your website. You don't want these advertisements to intrude on your visitors experience navigating throughout your website, but instead focus on creating advertisements that fit well within your template and use a similar color scheme.
Start with the 250x250 square ad boxes or the 300x250 medium, size if your blog's theme can accommodate it. Otherwise, the tower advertisements can be integrated into the side panels of most blog themes.
The 728x90 leaderboard ad box is great for the upper portion of your blog's theme, right under the header, or at the very bottom, featured within the footer area of your website.
Monetizing Your Blog With CPA
CPA can be extremely profitable, but it is also tricky. Choosing the right ads is very important, keeping in mind you must monitor CPA campaigns very closely.
Most CPA campaigns only last a few weeks to a few months, and they can be removed without any notice at all. Because of this, you have to continually watch campaigns and change them when they become inactive so you don't lose money.
CPA Lead, Hydra Network, Advaliant, Never Blue, and Max Bounty are just a few programs and networks I recommend to help you get started today and start making money online.
If you don't have a blog yet, I highly recommend starting out with blogger.com. It's easy to use, completely free to use and compatible with google.