Engine mis fires badly

start with an ignition up grade , plugs, wires , coils , if they are bad replace them , scan for codes , you may have to get codes from the dash board

Is the check engine light on? If so get the vehicle scanned for trouble codes. This can be done at almost any auto parts store near you at no cost. When you get the codes do some internet research on your particular vehicle and the codes that came up. This may point you in the direction of a cause of the miss-fire.

Yes codes, even if engine light isn't on take it and have someone that knows how to read one check it for you. If no codes stored than just look before you replace anything. Look for cracked plugs burnt spots on plug wires or corrosion especially where their touching any metal. Pull off distributor cap and inspect. You can also check plug wire resistance if you own a meter. A little time and a closer look at your engine before part replacement may save you a lot if money.