Hi,
Could be many things but if it were mine and I was trying to avoid a garage bill I would start by replacing the Spark plugs, then the leads including the plug caps under the coil packs, then if the fault was still there I would try swapping around the coil packs to try to eliminate the misfire.
But its a lot less hassle to get the codes read on STAR, and be told what the fault is and possibly cheaper too as you would only have to buy the part that is required.