There's so much that I would do differently if CoH returned.
First off, I would actually get a toon to 50 before letting my altitis take over.
Second, do all the things I never did: inventions, mission architect, and auction house. Maybe have some folks help me understand it better. Which leads me to...
Third, I would team up more, join a SG, stop being such a lone ranger. I loved playing this game, but I solo'd all the time, unless my girlfriend at the time was logged on. When she and I broke up, I only solo'd. I was kind of shy, so I avoided contact with people. On the rare occasions (honestly, I think those occasions can be counted on one hand) that I did team up, my experience was lovely. But I was still too shy to actively team.
Fourth, spend more time on the chat. Be with people. Communicate. Become an active part of a community that I did not even realize, until after the game was gone, was so incredible.