STR points = x
INT points = y
Using a 2:1 hybrid int as example,
y = 2x
(2 INT points to 1 STR point)
Now, as at lvl 90 you'd have 267 status points,
x+y=267
Points spent into INT + Points spent into STR = 267
as y = 2x; and x+y=267:
x+2x=267
x=267/3
x=89
Which means you'll have added 89 STR points at lvl 90.
And as y = 2x; y = 2(89); y = 178, so 178 INT points at lvl 90.
Now, there are basically two ways of getting this ratio, one of them is to calcualte it at a caculater such as bobtheveg or the ones at nivlam, I personally prefer this one:
http://bobtheveg.dyndns.org/sroprofile/Then after spending the status points there accordingly, memorize the physical and the magical balance and everytime you level throughout the game take off all your equipment which has INT or STR blues, so to get your "naked" balances and level your stats accordingly so to get as near as possible or exactly to the balances you got at bobtheveg.
An other way, which is easier with some ratios and harder for others, is to each time you level add a certain quantity of points, such as in this case, a 2:1 hybrid int, knowing that you get 3 status points each level up, all you have to do is add 2 of those into INT and 1 into STR.
Also, it's possible, to with a build which has a ratio of like 1:9 at 100 cap, which means you'd add 30 points into STR, which then means exactly 10 lvls of STR (each level you get 3 status points; 30/3=10), and you can add these 10 lvls whenever you feel like, like from levels 70 to 80; or from levels 75 to 80 and later from 85 to 90. Do you understand? I hope it's somewhat easier to understand now.