Those are the worst.
On second thought its their kids.
First, I’d cancel my apartment lease, and move all my stuff into some nice part of the other world. I’d likely spend most if not all of my time there the first year or so; exploring and searching for exploitable technology/valuable objects/interesting locations would occupy my time quite nicely.
Since I’m single and no family, the only people who would notice me missing are my close friends, most of whom would be asked to join me. The others would assume I’m on vacation or something, I guess.
At this point, I’d do one of a couple things, depending on what I’ve discovered.
If the other world is safe, but just empty, and things look to stay that way a while, fine. Otherwise, determined by the threat level, I may just close the door and never look back.
If I haven’t found enough stuff on the other side to satisfy my greed, I start using the portal ability to rob banks, fort knox, jewelry stores, and the like until I’m fantastically wealthy… storing the good stuff on the Other Side, and using it to buy… I dunno, whatever that world doesn’t have that I want, I guess.
Once we got the other side established enough that we could travel across the whole globe, I’d divvy up the continents amongst my friends (I get first pick, of course, and the continents would be leases, not gifts!) to rule as we will.
Then I’d travel the world (the real one) and start setting up permanent portals in various locations, far too many of them for anyone to find them all and shut them down or seal them off. “Bring me your tired, your poor, your huddled masses, yearning to breathe free” and all that… “This way to Phnordtopia!” signs, to repopulate my new world. No Assholes Allowed (excepting me, of course.)
Then, once I have a happy, populated, well-organized and efficient high-tech society…
…we’ll start thinking about what to do about the problem of Earth Prime. 
Think: The Most Dangerous Game.
On another planet.
With Segways.