The first step in identifying an ancient coin is to work out what language is on it. You've basically got four options:
Latin: the coin will be Roman, or in a few instances perhaps Roman Provincial. There's also the possibility that it could be a mediaeval European coin with a similar design to ancient Roman ones. Since English uses a slightly modified Latin alphabet, Latin coins are easy for us to read.
Greek: Greek colonists founded cities throughout the Mediterranean, and the conquests of Alexander the Great brought Greek to places as remote and exotic as Egypt and India; sometimes countries even further afield such as Axum (Ethiopia) and Arabia used Greek too. It was the general "trade language" used on coins until the rise of the Roman Empire. Coins with Greek on them are still broadly categorized as "Greek coins", even if the people who issued the coin weren't actually Greek. Many Roman Provincial coins also bear Greek script. When reading Greek coins, beware of "false friends" - Greek P is actually an R, Greek H is acually a long E, Greek X is actually a Ch, and so on. Familiarize yourself with the
Greek alphabet, particularly the capital letters since they're the only ones you'll see on ancient coins.
Some other language: Ancient coins with a language other than Greek or Latin on them are very much in the minority: Pre-Roman Spain, Carthage, some regions in Turkey, and some of the post-Greek states in India and elsewhere. Many of these old scripts are not well documented - some are known only by their survival on coins - and finding letter-for-letter translations can be difficult.
Coins with no language on them at all, or coins where the legends have been made unreadable by wear or corrosion: these are hardest; the only way to pick them properly is to be broadly familiar with the various styles of imagery used in different parts of the world in ancient times, and use the references to try to narrow it down from there. Coins with a portrait (eg. Roman) can sometimes be recognized by distinctive features on the portrait, eg.
Julian II is the only Late Roman who might be found with a long beard.
Once you've got a block of text, or even just a few letters in sequence, try running it through the
Wildwinds partial inscription search.
Once you've been able to identify the basic type, to make sure you're attributing a specific type to it (eg.
RIC Hadrian 202), you really need the specific reference works for that series.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis