When you've properly captivated your audience in your learning of how to blog for profit, it's time to work on your overall design.
Unless you've bought one of those $500+ full design packages, you're not done with your design.
Take a look at Darren Rowse's blog (ProBlogger).
His front page design is very organized, displays all the correct info that people want to see, and is very attractive.
Now take a look at those free themes available from the WordPress theme site.
Those are very typical.
It's always going to be content and one or two sidebars.
The sidebars are just one big thing or widgets you can move around.
Honestly, I wouldn't want to see that (EVER!) on a blog.
I click away when I see that.
It's horrible design.
What you want is proper optimization so that ads can be integrated without any sort of problem.
But no worries! The Wordpress AdSense System actually will help you with that.
It takes those free themes and transforms them into something phenomenal.
Ads and design are absolutely no problem.
This is pure aesthetics.
Modern age calls for organization and cleanliness.
People naturally shy away from clutter and very messy/flashy designs.
Think about what you would want to see as a reader.
At first you might say "Ahh it's no big deal", but really think about it.
It's important.
Once you finish your design, which is basically playing around with a free theme (CSS isn't hard), you should have a strong base for your continuance into profit.
You've got the correct design, which makes readership building easier, and a small but solid readership, which can easily snowball.