I usually start with the metal, either as the word (bronze) or the symbol (ae). Usually it's pretty clear whether the coin is Greek or Roman, so I include that. Any discernible letters will narrow it down further, as will including some description of the image (i.e., "horse standing right"). Diameter and weight can help, but since especially in the case of Greek coins, these varied within the same coin type, I am cautious about using them. In that these are from various auction houses, it helps to have some familiarity with how the auctioneers typically describe coins. Obviously the more detail you can provide up front, the more focused the results will be. All that said, I do not always find the coin, and sometimes there is a certain amount of serendipity involved when I do find a match.
CoinArchives is another good general source for information on current and past auctions. When I entered, Philip I Viminacium coinarchives, in Google Search, and clicked on the image or entry, this was the result: https://www.coinarchives.com/a/results.php?search=viminacium+and+lion&s=0&results=100 The results include coins of Philip I and other emperors.