There's a couple of factors that might be at work here. One is whether your Next Actions are really Next Actions: it's fairly common to have things creep onto the NA lists that aren't really actionable. The result is that we tend to ignore them, because subconsciously we know that there's no action there. So going through your NA lists with an eagle eye might help. Getting real, actionable, NAs takes practice, and it's something you have to consciously work at.
Aim for action verbs with definite subjects, like "Call BugsRUs on 555 5555 about bringing some more cockroaches, because I'm running out" rather than "Call bug company", for example. Anything that's not completely defined is a warning sign. Any verb that can't be identified in a photo is a definite worry: things like Complete, Research, Investigate, are all non-action.
dschaffner has already talked about making a clear distinction between Active Projects and Someday/Maybe. Try to be as disciplined as you can about your active projects, and only let something get on the list if you're totally committed to it, and you're committed to acting on it within the next week or so. I have a Pending Projects list, for things that I'm committed to, but know that I won't get to in the next week: it keeps my NA lists clean and short, and ensures that I get through my less-urgent stuff at a reasonable pace. Before I had the PP list, I was finding that some things stayed on my NA lists for weeks/months, because there would always be something more urgent (which doesn't mean important), and because the lists were so long I went numb to them.
In short, keep your NA lists short. Be ruthless!
The weekly review is also helpful: it means you get a chance to evaluate the week that was, and tinker with the week that will be. Use it not just to bring your lists up to date, but to notice what you're doing, what you're not doing, and why you're doing/not doing.