I just try to make sure that when I'm not feeling particularly super-interested in my tank that I'm not completely neglecting it. My first tank was back when I was in high school, and being an irresponsible kid who wasn't ever home anyway, I let it be neglected/ evaporate out to the point where the tiger barbs I had in there (that hadn't killed each other) were swimming in who knows what kind of toxic goo. This is pre-internet, and in the days of undergravel filters, too, so I bet it was terrible. Oh well. Didn't know any better, and I just shared that story because I remind myself of that now when I get complacent about my tank. The critters in it are living creatures, and even though they don't interact quite as much as my dog (at least they don't jump all over me and chew on me, though), they deserve just as much care, or at least enough not to have to live in terrible conditions while I am being lazy or disinterested.
Last week, I cleaned the tank out completely, scrubbed all the decorations, shocked the plants in ice water treated with Had-a-Snail, split my Java fern, and put some new mondo grass in the back. That only took about an hour, and the tank looks lots better. I do a little bit of that kind of stuff now and then to stay interested.