Combine 3 grams of instant coffee of choice with cold water and mix, allowing to dissolve. This may take a long time. You could speed this up by adding a bit of hot water, allowing it to dissolve, then adding cold water the rest. You want the coffee ice cubes to be pretty dark as they will lighten in color when they freeze. Try to only make as much coffee as you will need for an ice tray, but if you have leftover, you can add it to your iced coffee mix.

Add 9 combined grams of instant coffee to a heat safe receptacle with a lid that will fit in your fridge. Mine was about 28 oz so that's the ratio you're working with. Boil water and add any sugar you will want now so it will dissolve and you don't have to make simple syrup. Here is where you add any flavorings you want.Add as little water as you can, enough to dissolve everything. Pop the lid on and shake.

Once dissolved, fill the rest of the way with cool water

Freeze ice cubes and chill iced coffee overnight. I make this a day in advanced

Depending on the size of your icecubes, for around 12 oz of coffee, I add 1-2 standard sized ice cubes. Coffee is oily so if you add too many, there will be a very unappetizing oil on the top of your coffee that won't wanna mix with the rest. Smaller ice cubes is better

Optionally prepare it this way:

Add any cream or whatever you want and enjoy!