Based on the above data, a mix of 3 odds and 3 evens are okay, as well as the ratio 2 odds and 4 evens, or 4 odds and 2 evens. However, you cannot put aside that from time to time, a ratio of 1:5 or 5:1, though rarely, can also become true.
If you want to cover all probable ratios, you can play 12 lines (12 combinations) where 4 of them have the 3:3 odd-even ratio. See the column To Play. Depending on your budget, you may play fewer lines. If you opt to play 10 lines, play 3 lines of 3:3, and 2 lines each for 2:4 and 4:2. If you opt not to play the 1:5 and 5:1 ratio, you may play 2 lines for 3:3 and one line each for 2:4 and 4:2.
Where do you position the odd and even numbers? Based on probability data, the position of the odd and even numbers are not that significant. The variance between one odd-even pattern to another is very minimal.