Good writing, #1. If a blog is not well-written, people won’t want to come back. The writer needs to have a good command of the language, and know how to use it effectively.

I’ll go with 5 characteristics.

1. Great content.

2. Good design (or at least clean design).

3. An author or authors you can learn more about.

4. A blog where, when you visit for the first time, you know pretty quickly what it is about.

5. A blog with a great community that creates meaningful discussion in the comments.

• Ritership
• Readership
• Relationship

Being new to the hole blogging aspect of socializing. I think that if you are to have  sucsess in any blog ther  must be an objective, or reason the average person won’t wast time reading for no reason.

I like to preach quality and consistency. I am just starting my own, so at the moment I know that I have neither. But for the blogs that I have managed, those two things were always key!
Quality in writing, content, and photos (man, do I hate photos that are not the full width of the space, or ones that have really poor resolution or are distorted).
Consistency is really key (in my opinion). I personally keep an eye on the blogs that I like via Google Reader. If you aren’t posting at least 3 times per week, I have no need to follow you anymore. 
That’s just me, of course. I do agree with everything previously written as well.

As this is for a successful blog, I would assume its:

1. Relevant topics
2. Consistency
3. A community who interact
4. An author who interacts
5. Large numbers of social shares
6. Large numbers of daily visitors
7. Large email subscriber list
8. Reader advocacy
9. Great copy writing skills
10. Content that drives action

I also agree with the points mentioned above (e.g. professional design).