How to determine your Interests
Although you can still use any tag you want when you publish a post, the platform itself will be more and more oriented at interests.
Your Account Interests
The place to set these interests is in your wallet.
The interests to choose from are the same interests listed in the right sidebar when you are browsing your feed.
More than a few people have already mentioned, why only 5 to choose from, I have way more interests. Interests however are not what you want to read about, but what you are writing about yourself.
For example, user x sets an interest in art, but just because he likes to look at what other people create, not really an artist himself. User y searches for people who publish art, just to look at it, finds user x, and starts to follow user x.
Neither of them however posts about art. They come across each other's posts in their feed, and decide to remove after some time because you have nothing in common.
So, for your own account you have to set your interests to fields YOU WRITE ABOUT.
How to find people with common interest?
The menu in the left sidebar has a "Discover People" option. At the top of the Discover People page, there is a filter you can use to limit the list of users displayed by selecting an interest.
Another way to find people is by visiting the accounts of people who post comments to posts of users you already follow, or are friends with.
Your Pod Account Interests
For your pod account it may be a bit easier because you focus on an interest already.
For pod accounts there are two places to set interests. One as a regular account, and one as a pod account. My advice would be to set those to the same interests.
Use your witness votes wisely
Jump over to the Block Producer / Witness page and cast your witness votes. Simply click on the (^) up arrow next to the witness names of your choice (consider voting for "krazywitness" and "ijmmaiwitness") and supply your private active key to lock in your vote. Refresh the page in case your vote doesn't seem to stick.