I've found that by putting an estimated time next to the next action (paper based for me) helps a lot. When your feeling slack just grab your current context list and say to yourself 'ok, ive got a clear half hour I'm gonna knock out those two 10min items and those two 5 min ones' for example, set a stopwatch/timer and go for it allowing yourself to stop after the time runs out guilt free or when your done. That'll give you momentum and before you know it you've done a couple of hours work and your flying.

It really works, kind of like a big two minute rule, if you get what I mean!