There's a number of ways to support dahlias, its really a case of picking what suits you best for your situation- like everything in life, there's no one size fits all solution that covers everyone so try a few out and see which you prefer
I personally use multiple methods depending on which garden they're in.
METHOD 1 TRIPLE TIE
For my large dinner plate-sized dahlias that co-exist with other plants, I use the singular stake method. I dig the hole then place a stake of at least 1.2 meters firmly in the hole before I plant. As the dahlia grows I tie it on using - don't laugh - shower curtain clips (photo 1). I do this three times as it grows so that it's completely supported.
METHOD 2 ZIGZAG TIE
For the dahlias that I plant in a hedge, I use a triangular staking method using bamboo and fabric tyes. As always, dig all the holes first. my rows are a meter wide and 5 meters long. each row has a pathway in between to allow room to maintain them. The beds are planted two dahlias wide and 20 inches between each dahlia running the length. Place one stake on the outer edge of each dahlia hole so you have a row of stakes running the enter outside length of the row on both sides. Now, starting at one end and working down, place a stake so it is off-center to the other two stakes, it should form a triangular shape when combined with the outer stakes. see photo 2. Then, using my fabric tye, I run it around the poles to form a triangle and tie the two ends together - not to the pole itself! This gives you the ability to slide the ties upwards as the dahlias grow. Remember to be careful to not overlap your ties or it won't slide. See photos.
METHOD 3 CORRALING
Another popular method is corraling the dahlias. Using pairs of strong waratahs/stakes at either end of the bed, the grower runs a wire/rope, etc from one stake to the next lengthwise then ties ropes across the width, forming tight straight gridded lines to support the growing plants.
METHOD 4 NETTING
Netting horizontally is another common method that works well for a number of cut flowers. I personally found it made deadheading and harvesting really hard so won't be doing it again this year.