I'll parrot a lot of what Bushy said, but to me it's staying on long term, or never coming off. You don't need super long cycles, or the blast and cruise approach unless you are a competetive BB'er. Recovering is absolutely necessary for the average user to stay in the game long term while remaining healthy and without long term, nagging/lingering effects. While on you feel and look great, but it's important to remember that when off you will undoubtedly lose something, but you gotta stick to the plan to recover no matter what games your head is playing with you. Falling in love with being on, to the point where you need to be on just to feel normal or adequate is a trap tons of guys fall into.
As BBB also mentioned, using compounds which alter your behaviour. It does happen, and for me, it's using tren. I love the body comp effects the stuff promotes, but even at low doses it is not agreeable with me. I value my relationship with my wife and kids so I steer clear. It's probably different for each individual, but I think it's important you know how you react to certain things and to evaluate the risk vs reward.
Using super high doses. Again unless you compete (and even to a degree if you do) you usually need less than you think. After doing this for several years and learning all along the way, I've found that less is generally more. I still run about a gram of total gear, but it's usually divided between 3 to 4 well thought out compounds (for synergy), and I have found my results are better with much less negative sides. No more 2 grams of test, or a similar number of a couple compounds for me personally. I used to think my sweet spot was in the 1200-1600 mg range of total gear, and back then it may have been, but as I've learned to train more effectively and time my nutrition better I find that I do better with right around a gram total. The benefits are still great,and the side effects are less pronounced and much easier to control with proper ancillary use.
I've been guilty of all of the above at times, but have learned through trial and error, plus personal experience how to put it all into perspective and feel better than I ever have at this point. Your mind is quite possibly the number one thing that you need to have control over to avoid falling into the "abuser" category.
I probably haven't said anything life changing or ground breaking, but just thought I'd share my POV.