If you are American ($) or European (€), then you are in luck. First, the exchange rate is very good today (January 2017). Second, you can get either dollars or euros from ATMs. Why would you want to do this?
When you get Georgian laris from the ATM, you get the bank exchange rate, and your home bank charges you up to 3% in “foreign transaction fees.” So, get dollars or euros from the ATM, then exchange your dollars or euros at one of the many currency exchange vendors who do this. They are very visible on the street, always with big neon, red exchange rate signs showing you the buying and selling price for various currencies.
WARNING: There are many unscrupulous currency exchange booths in the most touristed areas. They will charge you up to 10% in commissions! This is totally wrong. AVOID the touristy places (Old Town, Marjanahsvili, Rustaveli) when exchanging money. You should see a visible sign outside of the exchange window telling you the commission fee (if there is one). BEWARE and pay attention.
Almost ALL of the exchange booths in Tbilisi charge NO commission and the spread between the selling and buying price for dollars is less than 1%.
So, get your dollars from the ATM, go to any currency exchange booth on the street and convert it to laris. Then, if they give you any notes larger than 50 laris, go to the first bank you find and change the larger 100 lari notes into 10’s and 20’s.
You will only be able to use the larger 100 lari notes at major restaurants and the larger grocery stores. In no event should you get into a taxi without the correct change. They will almost always tell you that they have no change, even for very small notes. Get in the habit of saving your one and two lari coins just for the taxi.