There is no "correct" pattern, but a very common one, seen on 6-sided dice, and sometimes extended to higher-sided ones is to pair up numbers on opposite sides.
For 6-sided dice it is normal to have sides paired 1,6 / 2,5 / 3,4, each pair adds to 7. There are two different ways of having this arrangement. If you take a large number of 6 sided dice from different sources it is very likely you will find you can group them into two sets that both follow this arrangement, but which vary in how you can rotate them to match.
For 8-sided dice, it seems common to have sides paired 1,8 / 2,7 / 3,6 / 4,5 but I have seen exceptions (which are generally fine, you should not be concerned if it is not true for a die you own). There are 16 possible to arrange those pairings, see below for a full list.
For why this arrangement is common, many sources claim that it helps to keep averages correct for imperfectly-shaped dice. If your 'cube' is shorter on one edge, it would favour two opposite sides - if those sides don't give you an overall advantage, this is seen as fairer. Although it may also have been driven by numerology, and the design kept by tradition.
Identifying D8 variations (those with opposite sides adding to 9).
Rotate the die so that you are looking down onto a point with the 1 at "12 o'clock" and with
the 2 at either "3 o'clock" or "6 o'clock" (one of these positions will be possible, if not then
you have already got 1 and 2 on opposite sides, which of course makes the total 3). Read the numbers, starting
from the 1, in clockwise order.
The following variations are possible:
These variations are the complete set for opposing sides summing to 9. It is not possible to take one of them and then rotate the die so that it exactly matches another one.
If you see one of the above variations, it does not prove that the opposite sides sum to 9. If you are not sure, then you need to check that also. And worth repeating: It is not a problem if you find a d8 that does not have one of the above patterns or does not have opposite sides sum to 9.