I sell old (1890 english pennies) to mid 1980s coins mostly. It all depends on the country, denomination, grade to collectors or what is on the coin to other collectors. Pictures of animals sell well for example.
As for price - I look up everything in my 2012 world catelog. I do this to double-check the content of the coin for one. I then take the lowest grade price unless the only price is for Unc / Proof coins. Most of the coins are $.25, then I'll find a few that are harder to find and worth $.25 - $3.
I put all the coins in a 2x2 flip with the country and price on it. The coins also sit in a metal coin bank. So I get lots of interest from people looking for US silver, but also attracts the attention of mom, pop, or grand-dad who buy them for kids/g-kids. Few collectors come by to see what I have to fill holes in their albums.
I have number of world bank notes that I may start selling also. May pair them up with other coins and put them in some of these picture frames I have totes full of and sell as "sets". So instead of $1 or $2 I can sell at $5 or more. Plus, get rid of some picture frames.