My stock tables are something like:
-100.00 -100.00 -100.00 -80.50 -61.10 -41.30 -21.60 -19.00 -11.00
(from coldest to warmer, I didn't include all the columns.)
I multiply that by 0.xx (something less than 1)
Like multiply by 0.55 results in:
-55.00 -55.00 -55.00 -44.27 -33.61 -22.71 -11.88 -10.45 -6.05
Which results in MORE fuel at cold temperatures between keying the ignition and warm-up of the O2 sensor and a switch to closed loop.
Since my ROM has -100 in the coldest columns, it's easy to see how much I've adjusted by, since the coldest columns are always equal to the % change I made to the entire table. Start with a pretty big change, like multiplying by 0.6 or something, then make changes in 3-4% up and down the next couple days and note which direction to head to get better.