1. Stop reporting hacks, dupes, and exploits. I'm not suggesting any of you actually go out there and hack, dupe, or exploit things - but when you come across it, don't report it. The more of this we have, the more D2 like the community will get.
2. Accept all the spammer friend requests. D2 had a very strong social component, and one of the staples of that was constantly being spammed for 3rd Party Diablo 2 websites. But we don't experience that as much in D3 because we don't accept friend requests from the spammers!
3. Pretend you have a stamina bar. Every now and then, stop running and just stand there for a moment.
4. Reroll a new character every time you want to change your build. Just because you don't 'have' to reroll a new hero doesn't mean you can't. If you want to switch your monk to a tempest rush build, make a new monk and revolve them around tempest rush!
5. Don't bind any skills to your left mouse button. Just leave it empty so you can basic attack everything all the time.
6. Don't use the AH. Just try to sell everything in chat. And only buy things in chat.
I hope this helps other diehard D2 fans get a little closer to that feeling they've been chasing since D3 launch!