One of the best ways is to blast clean,if you go on ebay you can buy a small battery powered blaster,thease are no longer made,i remember them in the shops years ago,never tried one,but I got a old unused one,it works well,they work off of a 12v battery,as in car etc,they were fetching a fair price ,don't know why,but does the job fine,just put in ebay search sparkplug cleaner.
Goldman