Don't play online too much, you'll ruin the game. Trust me, I did it before and regretted it so much that I reset.
I would recommend:
- Don't sell your tbt. You start with 1000 and 100 is worth up to 20 million bells. It may be tempting, but what's the point of playing when you have everything within your first day?
- Limit the amount of villagers you adopt (check the Villager Trading Plaza). Try adopting only one villager (must be free) per week or two, or something like that.
- Only ever buy DLC and foreign event items -- don't buy anything you can obtain in your own game, including hybrids, saplings, and bush starts. Pay for these iteme with your tbt bells so you don't have 5000 within five minutes.
- Play online with people and do tours and stuff! It's fun!
- Don't sell your items, since a lot of people here give waaaay too much money since they either supe or unintentionally trade with dupers/people who traded with dupers. Giveaways are cool though.
- Decide whether or not you want to time travel. It doesn't matter if you do or don't, either way is fun.