This topic is too huge to be discussed in one post. These are quick notes only in a simple way:
You can check the performance of your blog through: Google Pagespeed.
It’s very important tool for those who are “Self-Hosting” their websites – for example through WordPress.org. I find it handy too in many other areas such as deciding on displaying ads on my “Hosted” blog.
One of the best statistics tool is: Google Analytics.
It’s free on self-hosted websites. However, it’s expensive on WordPress.com – Business Plan is required. WordPress provides its own statistics software that is a little bit simple in comparing to Google Analytics.
You can also check a different prospective of statistics on: Alexa Traffic Rank.
Have you ever tried any of these tools? They are very handy and you won’t regret trying them every now and then.