The best way to kill clover in lawn is to keep the grass at a short level and use a commercial product designed specifically for clover control. If you must get rid of the most common weed found in lawns, then look at the local garden store for a dicamba salt and a phenoxy herbicide mixture. To immediately get rid of the problem pull the clover up by pulling one plant at a time from the stem at the closest to the ground that you may reach. This is the fastest way to rid your lawn of the troublesome weed. Another way is to rake the areas affected forcefully.
Do not just work once on your clover problem. This is something you need to watch for and with continuous applications of treatment eventually rid the yard of weeds. Also, over seed the lawn with new grass seed as needed to cover any bare spots.