Hello!
Depends on how you want it to look. There is one near me with the full WRC bodykit and rear wing, looks daft as it is still sitting on the original alloy wheels, does it no favours at all. Do it in small steps, like lowering it on coilovers and changing the wheels for something sportier to give it a more sporty stance. Resist the aftermarket bodykits as some are really bad and do nothing for the cars looks, poor fit and finish etc. There are a few Focus owners on here who can direct you best.