How many times do you sim your character? I'm trying to find the magic number. I usually sim my character 10 times.
I do one of 2 things. I either grab the average numbers between all stats to get my stat weights or go with the weights that yield the greatest DPS increase. Is there a correct method between those 2?
Run higher iterations as said. Do not do any less than 10,000. I also tend to favor reforge plotting a little more than just looking at stat weights as well.
As mentioned, anything less than 10,000 iterations is generally going to produce inaccurate results - 10 is an incredibly small number (unless you're running X number of iterations 10 times, in which case you may as well just increase the iteration count).
Other than that, sim when you're getting new gear or make changes to existing gear, but that's a given.
That said - simcraft is only as good as it's APL (Which last I heard, demos was poor - afflictions wasn't making full use of procs, and destruction's % of damage done by ember consuming spell was off, which likewise throws mastery's value into disarray - though I'm not really number savvy to be able to preach about how good or bad simcs APL is), and warlocks newer play which seems to hinge on very "human" choices based on fight mechanics, means it's results should be taken with a fair bit of salt.