The best way to order from least to greatest is to make all the denominators equal so find the Lowest Common Multiple of all the denominators:
LCM= 24
2/4 (times 6) = 12/24
2/3 (times 8) = 16/24
2/8 (times 3) = 6/24
2/6 (times 4) = 8/24
Now you can easily order which is lowest to greatest (REMEMBER TO SIMPLIFY BACK TO ORIGINAL FRACTIONS WHEN ORDERING)
2/8, 2/6, 2/4. 2/3
Hope this helps! :D