If you feel demotivated to cook, clean, or otherwise leave the house. Try putting on "outside clothes" (i.e. not PJs). More often then not it will give you that little push you need to start doing the important thing
I tell myself that taking the first step (of whatever task I'm avoiding) doesn't mean I have to complete whatever task I'm avoiding. Somehow reminding myself that, for example, taking my socks off doesn't mean I HAVE to take a shower, gets me over the initial hurdle of resistance. If necessary, I will lie to myself about each step of a task, with full knowledge I'm only saying it to trick myself into doing something. At some point, I decide that I might as well finish (usually).