Did you clean the plug of oil? I'd pull cyl #4 plug (farthest on the right I think) and recheck your plug wire placement.
I just got my first Focus, first Ford I've ever owned. Previous owner had put the plug wires on wrong. Google search was all it took for me, and about 10 seconds later the car was running great.
I'd also replace the fuel filter and do the obvious checks (alternator, battery, tight belt, etc)