If your coins are valuable, you better not clean them, cause that will reduce their value.
(this is called cartwheel effect and because it is a chemical procedure i cannot explain it in details, sorry

)
Now, if you insist on cleaning them, the safest thing you can do is this:
1. Wash it under cols running water, holding it by the edges.
2. Soak it in vinegar for a few seconds to minutes, or lemon juice only if it is silver.
3. Wash it under warm but not hot water.
4. Brush it very very gently and lightly.
5. Dry it.
If there are small parts with dirt, you can remove it with a toothpick, but be careful not to scratch it^^
You don't need to rep me, i had the same question some years ago for my jewels.
Hope it helps ^.^