OmniFocus? Google Tasks? JIRA? What the fuck are you thinking? Technology gets in the way of managing projects. You know what works? Fucking paper and pens. Get some post-its and a flat surface. Divide the surface into 3 columns: "To do", "In progress", and "Done". One thing in the "In progress" column at a time. Write your task titles so they start with a verb. Now get on with it.
Really really can't make do with one thing at a time? Have different rows for different projects. But be very suspicious of multitasking; it's bad for productivity.