My advise is never clean your coins if you can avoid it, in case there  is no option but to clean your coins, heres what I do.   

I have 4 steps, the first is buffing them with a soft buffing cloth or a  terry bath towel / napkin   

If the coin still needs cleaning, then soaking in a soapy solution of  detergent and water. About 12 hours   

If you still need to clean it more, then soak in  a solution of lemon  juice and water. but make sure you wash it completely clean after.    

For the absolutely war like situation when a coin just wont get clean,  soak for 2-3 hrs in a solution of water with household bleach. BE  CAREFUL. It is highly corrosive   99% of the coins will get clean   

In my opinion , Do not use toothpaste since they tend to have a high  hardness on MohS scale and may scratch your coins. Dont use cola either  again highly anti coin friendly

All the best, keep safe