The first thing you should focus on is offering the most valuable content. Once you have the content then you have half of the battle won.
BUT what is your main goal?
1. Is it to make the blog popular on social sites, forums, youtube and other online platforms?
2. Or is your main goal search engine traffic?
If your main goal is number 1 then you're going to need a lot of content, mostly on a daily bases when you're just starting out. The more content you share on your blog and other online platforms the more you'll attract visitors and build a loyal fan base/following.
In order to attract a lot of visitors to your site using social networks and youtube, then you're going to have to share something fresh at least twice a day. Why twice a day? So that you can be able to reach more people in different time zones. So you'll need one post in the morning and another one in the evening.
When your blog is more popular and you've built a good following then that won't be necessary, 3 to 5 posts a week will be fine. But for a new blog, it's necessary to post twice a day so that you can grow faster. Don't focus on sending people to your blog when you're just starting out, focus on building your social media profiles.
Once you've built your social accounts then you have traffic on demand, you can post or promote anything whenever you want. The key to getting more traffic to your blog is to keep adding new people to your social media accounts.
The more people you add, the more traffic you get and this will also increase engagement on your social accounts and blog. Simply because new people/members are the ones who're always asking questions and they're the most active people.
BUT...
If you're going the SEO route then you won't need a lot of content or a big following on social media. All you need is to target a few profitable keywords and send strong backlinks to your site. The more content you add, the more backlinks you'll need in order to keep ranking high in search engines.
The reason you'll need more backlinks is because when you get a link from another site it will pass link juice to your site. If that link juice is sent to your homepage, then the homepage will pass that link juice to the blog and other pages on your site.
So the more content you have, the more the link juice gets spread and it becomes weak. But if the link juice is shared to only a few pages and posts then it remains strong and keep your site ranking high.
Can you do both number 1 and 2?
Of course you can, but always remember that the more content you have, then you'll need more backlinks. Most marketers will never tell you this or they don't know it and it's the most crucial thing to consider before starting a blog.
This is crucial so that you don't end up asking yourself why your site is not getting enough traffic, instead you'll know that you need to work hard on improving your online presence. Or ask yourself why your site is not ranking high in search results, instead you'll know that you have too many posts and the backlinks you acquired don't have enough link juice to get high rankings.
Which one do I recommend between number 1 and number 2?
I recommend number 1 for new bloggers because it's a long term strategy. SEO can change any day from now and your rankings can drop at any time. People are always improving their websites SEO-wise so you always have to compete, and new people are always coming in, so the competition is tough.
Even though search engine traffic is my number one traffic source for most of my blogs, I always create a loyal following on social media just in case anything happens.
I won't get into how to do proper SEO or social media marketing. I'll stick to your question which is what to focus on for a new blog so that I don't get off topic. But hope you get the point I'm trying to emphasize about knowing your end goal.
Another important thing to focus on is building an email list. Never put this for later, this is a big mistake lot of new bloggers make.
The money is in the list 
No matter how cliche that sounds but it's really true, with an email list, you can make money even if your blog is not generating a lot of traffic. That's if you're doing proper email marketing though and not spamming your list.
So the most important things to focus on is offering valuable content, knowing your end goal so that you know which traffic source you're going to focus on and most importantly, you need to focus on building an email list.
Hope that helps
