How to maximize horsepower in my 2013 ford focus SE?

Listen, I have a 2013 ford focus SE with 160 hp stock. Im trying to boost my hp up to improve performance. I have already got a injen cold air intake. I need other ways that arent to hard to do, or exspensive. I dont want to make my car look dumb, so dont say "add a cool loud exhaust and a spoiler." im not trying to make a not fast car, totally fast. Just boost the performance. So please, im looking for simple things i can do. The injen air intake was 270$ and is said to add 10 HP and boost fuel economy. PICKING BEST ANSWER FOR 10 POINTS.

Thanks!

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