there are two good methods of rolling for stats. Balls to the wall high variance 6d20 down the line after declaring race and class.
Or "roll 3 then flip".
To do the latter, you roll 3d6, rerolling any total result lower than 6. You repeat this process 3 times until you have 3 numbers between 6 and 18. For each number, find it's paired number.
18,6
17,7
16,8
15,9
14,10
13,11
12,12
Those paired numbers are your additional 3 stats.
So for example, I roll 3d6 3 times and generate 17,11,9
I consult the pairs, and get 7, 13,15
My stat array is now 17,15,13,11,9,7
There are some tweaks you can apply depending on how powerful you want the NPCs. You can add one to all the secondary numbers for instance (which ensures that stat rolls won't be all even or all odd). You can set the minimum and maximum values to different numbers (though the min and max should always be equidistant from 12, unless you're changing the average). You can change the dice rolling method while keeping the min/max and flip. This would be if you want the results to have different weights, perhaps weighing 15/16 and 8/9 more heavily than middling numbers to avoid "average" pcs.
With this method as is though, all stat totals will add up to 72, the average stat will be 12 for all players. Modifications are only meant to be undertaken with known goals in mind, because no one stat rolling method will actually solve all desires of every DM and every player you morons. You're all debating different things and I'm surprised that decades into the lifetime of the hobby you idiots haven't realized that some people like variance, and some people like balance, and both are valid goals in the pursuit of fun.