This recipe is not exact, but trust me, go on your own taste and it will turn out to be the best tzatziki you have ever tried. I have learned some tricks to make the tzatziki turn out beautifully and I will teach them here.
Peel, deseed, and grate the cucumber in the SMALLEST possible grater you have (food processing is also ok). Drain all the water you can from the processed cucumber. This can be done with many different methods. My favourite is just using my hands and squeezing the water out. A sieve or fresh cloth can also be used. Grate the garlic as finely as you can.
The yogurt used in tzatziki is actually thick or PRESSED yogurt.
If you cannot find this use regular yogurt and but a cheesecloth. (if you cant find a cheesecloth just use a piece of fabric with small holes). Put the yogurt in the fabric and let it hang over a tub. The water from the yogurt will drip out and after a few hours you will have a thicker yogurt.
The lemon juice and vinegar both add acidic taste to the sauce. Adding both of them adds acidity with two different flavours (making the sauce better than just using one). You can use just one or substitute either for the type of vinegar you prefer.
The olive oil in the recipe though it is in a small amount makes the sauce creamy.
The dill, although not needed, adds another "unknown" flavour to the sauce which adds to its complexity.
Do not BLEND the yogurt. I have read on reviews of other tzatziki sauces that the sauce has turned out runny. BLENDING YOGURT turns it into milk. Do not do it.
A lot of people recommend that you leave your tzatziki for a few hours in the fridge. I don't really do this (as I always just make the tzatziki when I crave it).