Let's answer your questions regarding blogging.
1. In order to blog for money, you have to first start blogging. And to make money you need specific niche under which you need to blog. So if you're a foodie blogger then you can make money by guest posting, content writing, displaying affiliate ads and also by posting sponsored content. So it all starts from you creating content on regular basis on your own blog or any other platform.
2. Before you start, you need to learn how to write content that convinces people. Also your writing must include either image, video and audio. Once you get good at the writing blog posts you also need to understand few technical terms such as CMS (primarily you'd work on WordPress or Joomla). So you need to have some knowledge of those CMS. Apart from that little knowledge of SEO and Social media definitely helps.
3. Before you start blogging here are some of the things to do. First thing to do is - choose a niche that has enough competition and advertisers to make you money. For example, photography niche has both advertisers as well as customers to click on affiliate links and buy products or click on ads. If you choose the wrong niche such as information on how to recharge your mobile or how to recharge TV subscription, you won't be making much money. Second is the name. your blog needs to have catchy and easy to remember name. If you get enough traffic then you can buy the domain too. But not required in the initial blogging phase. Third thing, titles of your blog post. They are the one that brings the traffic to your blog. Fourth thing is promotion, you have to promote content on social media and other sources such as mobile and emails. These are the things you need to know before and after you start the blog.
4. There is no best way with adsense. With adblockers around, the earning from adsense is reducing every day. So as long as you are writing content on topics that gets you clicks, you should continue. Adsense earning requires some specific strategy though. For example, placement of the ads, traffic and the users from specific nations that have better CPC and CPM value. That's what decides the earning from the adsense ads. In case of amazon, flipkart and other affiliate links, your content decides the earnings. Your copywriting skills will have more conversions with affiliate marketing articles. It takes time for affiliate marketing to work but once it starts, you'll find the conversion revenue that earns more than adsense or any other sponsored ads.
Pros of Adsense -
1. CPC value is high for some specific niche.
2. Passive earning if you have lot of content.
Cons of Adsense -
1. Adblocker is reducing revenue each year.
2. SEO and SMO changes can affect the revenue at any time of day or month.
Pros of Affiliate Marketing -
1. More revenue depending on the product promoted.
2. Passive earning if you are producing multiple niche sites and generating content.
Cons of Affiliate Marketing -
1. Requires hard work for content and traffic.
2. Success ratio can be low for some niche and affected by competition.
3. Requires more time to generate revenue.
Both of these sources requires work and can go down if the SEO and SMO efforts don't pay off. Also with adblocker changes, it becomes harder to make money in a passive way.